There's some people whose idea of "troubleshooting" is to just "shotgun" in new parts until the problem goes away, then charge you for all the unnecessary parts along the way.
The trick is how to avoid these types.
I hear you about the front mount deck.
I have a 61" front mount deck and I like it a lot better.
It's easier to get under and around things so less trimming is needed, and if the added overall length of the mower isn't a problem, it's a win.
I've been running Mobil 1 synthetic 10w30 in my Kohler 27hp that's in a Grasshopper for years and had no problem.
I use this oil because I have it around for a vehicle I have.
Should I not use this?