We used to run 50 to 80% nitro in our motors. If we did not use after run oil, it would rust the piston cyl. in a few hours. That was of course before ABC came along. We normally used synthetic/castor blends, but the nitro was pretty corrosive. I would guess the bearings didn't like the nitro either, but never noticed. That was 40 years ago when I was a kid. Just another comment, I used after run in a motor that I kind of forgot about, and it turned to tar. I couldn't turn it over at all, and it was quite hard to clean. The piston was down, and it turned freely with ball bearings, but the cylinder was black. I think I used transmission oil, or maybe 3 in 1. What's the lesson here? I don't know, but maybe I will turn over my motors every couple of years to check.