I have a 19 year old John Deere Zero Turn, 760. It was a demo model I bought from the dealership in 2005.
We replaced the engine about 5 or 6 years ago, about 400 hours ago, the Kawasaki they came with was apparently problematic, often caught fire, but we kept it clear of grass so that wasn't it, I honestly don't remember what the fatal flaw was with the first motor, but it was replaced with a Kohler to the tune of about $3500, which compared to the price of a new machine was the better option.
The master clutch seems to be an 8 year item, I've replaced it twice. Seems to be around $500-600 to repair.
We change the oil and filters and keep it blown off after mowing, but otherwise have abused it mightily on our 15 acres.
I will happily keep maintaining it, and even would replace the engine again if needed as it is a workhorse and that mowing deck is SOLID.
I have a friend who has managed to get not one, but two Kubota diesel lemon zero turns. But whatever dealer she has in NC is not so awesome.
I do NOT love the dealer, although it changed ownership and I will say the service department seems improved. I'll have to see about the sales department... They seem to not realize that just because I'm a petite woman does not mean I don't spend my own money. My husband will never buy a piece of equipment...he'll use mine, but he won't ever go shop.