Welcome to the Forum Thegoodearth. old tractors are made of good old heavy duty iron and are normally very easy to maintain. they are not as technologically advanced and so therefore less prone to break down.
Take my 1967 model 306 CU inch 6 cylinder diesel, Chamberlain it will run for four days at 2000 rpm and use 25-30 gals of fuel.
yes its noisy, yes my bones ache, but my she has character,
often its not the tractor you have to trust its the salesman.
old tractors were engineered to last, I personally do not trust the quality of steel that many newer brands of tractor (or anything else for that matter) is made from my opinion only but there you have it.
hope this answers your questions somewhat.
Cheers