You are confused!
We are talking about mowers, not bush hogs.
I've never had to pull any engine to clean the cooling fins on any Walker. Maybe on other mowers.
The question is towards the 26EFI or l/c Kubota engines.
I have a 92' Kubota diesel (old 16hp) with over 5000 hrs. on it with no major engine problems. I've had some electrical and fuel problems (connections, switches, injectors) but the engine is still strong.
I have a 2000 26 EFI with over 600 hrs. and it has never missed a lick. It is my machine of choice.
So much so, that i have a 2001 now!