Evaporust. It is easy on most paints. It took two days solid soaking in it to even begin to degrade prewar Marx litho. I would be fairly confident the motors winding lacquer would laugh at it. It can be found most anywhere anymore X-mart to big box DYI.
The water rinse etc. is no big deal if the metal is dried fast and fully.
For boards I'd just brush it clean, maybe wipe some Evaporust to work on rust stains. Same thing on the water. I used to throw cabinet video game motherboards into dishwashers (no soap...chlorine is bad). Relays and fans are a slight concern; open relay cases after, forced air at fans for 24hrs is usually enough. I always wait 48 hrs before introducing power again.
Penetrating and regular oils with brass brush agitation is the old school way, but I am not so sure how the plastic would like some of those, so that way I'd be breaking it down to parts for sure.
Oil will slow or even prevent rust creep.
