Questions about corrosion are probably more suited for the Corrosion engineering forum. I am unsure if you are asking for a cleaning (and protection) process for the existing bolts, or how to avoid the problem in the future.
For the last issue it all depends on the cause of corrosion, and where the corrosion has attacked, and how much damage it has caused. The cause can be atmospheric (acid atmospher, salt etc), galvanic (wrong materials against each other), other chemical corrosion types in addition to missing protection and/or wrong types of bolts.
If you want to avoid change of bolts to another type or material, 'sandblasting' by dry co2 might perhaps be an idea (protect windings), in addition to fluids for cleaning and protection.