It was mostly the early model Kohler courage's that had that issue... I believe they (Factory in china, i think) fixed the issues of the top crankcase cover bolts coming loose, i know another member on here (
@bertsmobile1 ) knows more on that subject than i do...
Another thing is that 33r877 briggs had issues with the camshafts (cam part 793880 changed to new 84005207)
failing due to poor hardening of the lobes, then again I'm not sure if the issue was resolved on newer engines, but i do know they upgraded the replacement camshaft in it and is available for purchase.
I have the Kohler courage 19 sv590 on my cub cadet, It's been bullet proof except for the carburetor needle failing, (Which in a way is a Carb manufacturer issue, not kohler, that's my opinion) it has 300 hours on it.
but really, any of the problems with the courage can be spotted and resolved, since i don't mow enough hours each year for the recommended oil change interval, i do it at the start of the spring season, when i do that, i remove the plastic cover and check all the crankcase cover bolts to be sure they're tight, i also remove the cover in the middle of the season to blow out the cooling fins, i check them then too.. takes 3 minutes. i also check for any signs of the valve cover leaking, takes 2 minutes ( i always clean any dirt and dust off around the cover so any leak could be spotted easier). That can be done while the engine oil is draining instead of twiddling your thumbs.
my 2 cents, if you want to wait on someone else's opinion you are more than welcome too, as there are smarter people on here than me.