I don't think you'll need it.
Last year...after 60 years of abuse...the ears on my gearbox busted off so I was determined to rebuild it. You just cannot find well-made bushhogs (or any rough cut mower...I use the term bushhog for this sort of mowing), so I set out to rebuild mine.
The gearbox was so thick, that we just ended up machining off part of the gearbox case, fabricating a new collar for it, and welding it back on. Then while we were there redid the bearings inside, and because they are standard get-anywhere-bearings, that was easy and had a newly rebuilt bushog for $300. No Bushhog Brand parts needed!!
Now it sounds crazy, $300 for a 60 year old implement when a new one is $600???
But if the old one lasted 60 years and proved itself to be robust, $300 for new condition is a bargain! I dont think you can go wrong on this Bushog deal, assuming the person is not asking an outlandish price.