You shouldn't have any problems with rust or paint.

Tone rings are detected magnetically. It should take a VERY long time for them to rust away to the point of failure.

I guess yours are flaking up and contacting the sensors. If that's the case then you could use your favorite rust inhibitor.

We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon