An observation about "parts": the meaning of that term is broad and comprehensive, and may have drastically different implications for each person. Generally, what I would call "maintenance parts" are readily and easily available. This means oil filters, air filters, and belts.
Many of the tractors use a filter cross-referenced to a vast multitude of Toyota, Honda, Subaru and a plethora other automobiles. Any automotive parts dealer will have several on the shelf. I have never heard of a Japanese tractor using an unobtainable oil filter. The oil to go into the engines is readily available too, and non-problematic.
Air filters are generally one of three types. A flatter round type, similar to that often seen atop performance carbureted engines, a cylindrical cartridge type, and the oil-bath style.
Oil bath styles require only engine oil to service, so are the most universally serviceable of all.
The cartridge types seem to be fairly universal, and are available in brand-specific (say, Kubota or Case) as well as generically. These are easily available at any tractor service facility, whether brand specific or
not. My local (urban) Wal-Mart does not have these. Many auto part stores do; they can order them for next-day availability if not.
The final type are the flatter type, and these are both more problematic and easier, depending on one's interpretation. Some closely resemble automotive filters, but actually are incompatible, and will not effectively filter air. The YM2000/240 series is notorious for this. However, with some foreknowledge and a tube of silicone, one can improvise an effective seal. This obviously is not recommended, but is possible. However, several good online dealers provide the correct filters at very reasonable prices, and since the YM240 was imported through Yanmar, dealers can order you factory brand parts that are known to fit.
Fluids are easy: motor oil is ubiquitous for these, as is antifreeze. Hydraulic fluid is generically available, as is gear oil. Grease is grease, (At least among classes and for our purposes) and if you can't find diesel, none of it matters anyway. Fuel and hydraulic filters are straightforward, too. The metal screens are intended to be cleaned and
re-used. Spin on filters, like oil filters, are generic. Fuel filters are generally part of a fuel bowl assembly that seems universal to most equipment. If yours is peculiar, they are easily replaced or updated.
Belts are compatible in width and length with other V-belts, so measuring or matching will serve to find equivalent maintenance parts.
In summary, there is no reason maintenance should not be done due to a "lack of parts."
What I would call "service parts" are normally expected semi-wear items.
These can be more problematic, but are, generally, able to be found. I include water pumps, alternator/generators, starters, tires and wheels, radiators, and similar things here. Most of these are, happily, either rebuildable, serviceable, or replaceable with functionally equal parts. They may be tougher or very expensive to find in identical components, but will not keep the tractor from being functional; it may start to look cobbled together, since it is.
Water pumps are generally not an issue. I haven't heard of anyone not being able to source something from an online retailer. Many share water pumps with other engines, or have rebuildable components inside. They may not be stocked, generally, by a local dealer. This actually includes recent production domestic market machines, too: a friend recently had to wait a week or so for a fairly recent Kubota L-series water pump (I think he has a 3130) from the dealer. There are some postings about people not being able to find a compatible pump, but often they seem clueless or unwilling to take advice. Rebuilding the pumps is usually an alternative, too. In case all other alternatives somehow fail, an electric water pump could be used.
Radiators usually require a service job if they haven't been properly maintained. A genuine radiator shop can be tough to find, but are still
around. They can rod out the core, or, for a price, recore the tanks. With a few exceptions, they are unavailable as replacement parts, but they could reasonably be adapted, in extremis, to use a salvaged radiator from something else. You will have a Frankenstein looking abomination, but it will work.
Generators and alternators are either rebuildable or replaceable. They are fairly generic. Mazda and Datsun alternators commonly interchange with only minor bending or tweaking. Others have adapted GM alternators with some more work. If you don't run lights, a battery tending float charger can keep your battery at proper levels of charge when parked, and no electrical power is required except to start the tractor. Most of
these are generic for years and across many different model numbers, so can be found through an internet search, too.
Starters are also often rebuildable. They are not nearly as universal as generators or starters. Some incorrect starters are known to be sold online, especially through online retailers for starters. Sometimes they have the wrong number of teeth, for instance. Legitimate retailers, such as Hoye, offer correct starters; they cost more, but should last forever. Most starter problems are because of other trouble, like poor battery power, lousy wiring, etc, and avoiding these trouble spots will keep the starter operable indefinitely.
Starters are generally expensive; some are worse than others. My Shibaura-built Ford 1700 uses an oddball starter. It is available new through New Holland, but is over $1000. When I needed one, I didn't feel like doubling the price of the tractor by installing a new starter. A rebuild was about $200, including being shipped back and forth across the country. Local rebuilders were unable to help me.
Wheels and tires are usually long lived, but available when they are worn. Tires are easiest, wheels can be harder, but are simple to adapt or fix with enough time and/or money. Worst case means buying a set of similar wheels and building an adapter plate to match bolt patterns. Any good machine will be happy to take your money for this. I built a dual wheel spool to do the same thing in an afternoon.
Finally, there are what I call "hard parts," borrowing the term from transmission rebuilders. This is everything else on the tractor. Gaskets, pistons, hydraulic pumps, gears, transmission castings, bearings, sheet metal, etc. These can be impossible to find, and are what people should mean when they say one cannot get parts for grey market tractors.
Where does one find a transmission casting? Some specialized sources
MAY be able to get castings, but they will be prohibitively expensive. Nobody has castings for the N-series Fords, either. If your tractor breaks there, then, it is ruined forever. You should part it out and buy a new one. Gears can be cut, for a price, but it rapidly becomes cheaper to just buy a new machine.
Engine rebuild parts, hydraulic and injection pumps, etc are sometimes
available. If you break a crankshaft, for instance, only some are available, usually Yanmar and Kubota. The others simply are not in business anymore. Some of the Mitsubishi engines are common, and found in Mitsubishi, Satoh, Case, and Iseki tractors along with other products. These are easier to find. A broken crankshaft in my Ford 1700 means it is ruined permanently. Head gaskets are usually available, even for rare things. Keeping the radiator and water pump in good shape should keep that from ever needing to be fixed.
Chassis bearings are usually available through a good bearing supply
house. Sheet metal requires a salvaged part, often virtually impossible to find, or far too expensive to afford. A fender for my IH 284 was over $4000 dollars when last I checked, so absurd I won't even say anything. Headlights and electrical items likely are not, but easily substituted with other components.
Steering boxes go out on loader equipped machines, but sometimes just from use/abuse. Yanmar and Kubota have available kits or replacement sets. I don't know about others.
Hydraulic pumps may be problematic, too, with some of the less common brands, but are conceivably replaceable by crankshaft driven replacement pumps after some replumbing.
So. What do you mean by parts and spares?
In sum, I wouldn't worry too much about a machine for which I can find rationally priced engine rebuild parts and a steering box. Most everything else is conquerable within reason. I would spend a few hundred dollars to rebuild an engine. I will not spend thousands on a broken casting. Don't mind driving horridly ugly equipment.
Sorry for the massive post. I talk too much.
