Mineral ATF is as petroleum as Kerosene is. If ATF doesn't wreck the o-rings, Kerosene likely won't either.

I dont go off of appearance alone if the bearings are suspect. After cleaning and a short run I then evaluate the bearings. If they feel gritty or make any noise whatsoever, I replace them. Of course if you find bonafide rust after cleaning, then don't run the engine and change the bearings straight away. If you tear an engine down for inspection and have most of the parts removed/disassembled, the. change the bearings out right then. Better to take an engine apart only once - especially if the engine uses a ringed piston.