Four-wheel drive tractor

Four-wheel drive tractor, the tractor didn't have any issues until a while ago, maybe two months back, the hub broke and I got it fixed lazily. After a while, I took it to the mechanic and he adjusted it. There was a bit of knocking in the engine but it was running. Now I've changed the oil and everything, but the hub broke again. The tractor has been used, honestly it hasn't even been a month, and the rest is all standing still. Price is negotiable.