Whatever he may owe anyone else is not an issue here. I am unsure why you would have picked this person to store your tractor as you sound like you know him pretty well. BUT with that said--here are the pertinent facts as you have presented them.

1) He kept your tractor under roof for seven years.
2) He used your tractor for seven years (hours unknown-but not inconsequential).
3) He paid for some repairs (amount unknown).

Since you derived some benefit by the tractor being shedded for seven years I would figure some value for that. I don't know how to value that--check with a local storage place and see what they charge per month. Try to determine how many hours the tractor has been used and assign a value to that. See what he claims for repairs (with real invoices to back it up) and total it all up. I realize neither of you are going to be happy whatever the number is but if you owe him something pay it and chalk it up to experience. And if he owes you I wouldn't expect to get it.

Or you can just go get the tractor and not speak to each other for the rest of your lives.

Either way I wish you the best.

BTW the t/a can be put back in the tractor.