A trick I learned about not long ago from another model forum for cleaning rust from steel parts is to immerse them in white vinegar and let it sit for a day or so. It works a charm but I wouldn't do it with bearings. I've never actually seen a rusted bearing but I've felt some that I thought might be rusted, either totally seized or extremely lumpy. All of them only had hardened castor in the races and, after cleaning, were as smooth as silk. I've cleaned bearings by soaking in warm water and dish washing liquid, acetone and in a small ultrasonic cleaner with a little CLR (Oil and Grease Remover) added.

Corrosion? THIS is corrosion . Luckily I had a spare crankcase .