The Ford 1700 was made up until 1982. You can look up basic info on any tractor ever made on TractorData.com. Yes, they were and still are real nice tractors.
As to the loader lift, it could be anything at this point. I think you should definitely confirm for yourself that it does work and then quits as the seller says.
That way you can also check that the three point lift arms work and then don't.....i.e. if it is something simple like a filter or air leak, then the three point arms should also work and then fail the same way at about the same time. You should also feel some lesser changes at that same time in the way that the optional power steering works..... if that was fitted. Most of those Fords that had loaders also got the optional power steering, but not all.
Those Fords used a simple series hydraulic circuit similar to most compact tractors then and now.
They do have a cleanable filter inside the sump accessible under a cover which is often overlooked.
If the tractor works well otherwise, and only the hydraulics don't work right, fixing hydraulics should be something within the ability of the average home mechanic. It is much easier than engine or drivetrain work. Still, I would allow $500 to $1000 just in case. The filters, any hoses, and changing out the special trans/hydraulic oil will cost a couple of hundred of that at least.
There are several old time members here on TBN with good expertise on that type hydraulic system.
So you will have plenty of good advice....
I am always suspicious when something doesn't work. If it really is so simple, it makes me wonder why the seller hasn't fixed it himself. I'm not shy about asking that question, either.
The most basic test I use when looking at a used diesel of any kind, is I want to see for myself that it starts right up when the engine is cold. If not, I just cross it off the list and walk away.
Luck,
rScotty