The 5020 Allis was manufactured by Hinomoto (as were many other brand names). I have the 29 HP Hinomoto (model E280) and as other posters have said, AGCO has a good parts stock. AGCO has dealers throughout the US and are listed on their site. The 29 HP and gearing give it plenty of power with good speed.
I have had mine since 1980, I have various implements with it and it seems like a strong little tractor. It can handle a fairly steep sidehill with all the wheels extended front and back. It is an excellent mowing, rake, and light discing tractor. I have the turf tire option which has smaller diameter wheels which are a bit of a problem with rough terrain, I am looking for larger wheels or tires. The 10 inch front rims are limited in tire size availability. I use mine to manure out barns with a frontend loader. It is helpful to counterbalance with a back box. With the front wheels the same width as the rear wheels it keeps from having to cut two sets of tracks and getting stuck when backing.
It is economical to operate and has an excellent hydraulic pump provided the fluid and screen filter are kept clean.
Now for the problems, it has no power steering which really builds armstrength when used with a front end loader. LOL
Do NOT put your thumbs inside the steering wheel on rough terrain, laying the thumb back is pretty painful.
Other than my son dropping an 80 ft cypress tree on it the tractor has held up well. More LOL This required a new left fender, seat and hood. I'm still trying to find a good used hood for it and a level indicator decal for the implements.
I recommend you give it a paint job because the factory paint typically is thin and wears off leaving rust.