Part of the incentive of leasing a car is having the dealer take care of repairs. Why would you risk your warranty to do the repair yourself? Also, you don't own the car.

If you BUY a tractor, you should be legally allowed to repair it yourself.

You're probably in breach of your finance agreement. A UK youtuber a couple of years back financed an M4, got some mods added, BMW finance called him up and said he had to pay the balance of the finance in 28 days.

He clearly didn't have the funds and was at risk of losing the car with all the added mods.

Nobody should consider they own a car if it's financed. But they are liable for the bad things that can happen.

It has nothing to do with warranties. This issue currently didn't carry over to cars at all (well not exactly) for the most part you are able to do your own car repairs. Parts exist, both oem and after market. You can even find instruction manuals. But this is not true for tractors.