I've flown behind MT propellers on DA-40s, Pitts S-2Bs, Extra 300 and 300LPs, Super Decathlons, and various RVs. Every single one of them has leaked grease. Every. Single. One. I've got friends with Edge 540s, experimentals, etc. that have the same issue.
From a performance perspective, MT makes a good product. From a reliability standpoint, they're the absolute worst. I hate to say that. My S-2B has an MTV-9 series prop on it.
These problems go back decades. Read Dick Rutan's book about flying Voyager around the world. They had an MT prop on the rear engine and it failed. Lost a blade, almost destroyed the aircraft. That was a custom build, of course, but if I had a dime for every story of a delamination, paint issue, accelerated wear, premature overhaul, or serious grease leak from an MT prop, I'd be a very rich guy...