Glyptal was developed ages ago for electric motors and the insides of various housings. In fact New Process Gear (New Venture Gear / Magna Powertrain) used to dip their iron cases in glyptal before final machining. We have cases that are over 50yrs old, with no degradation in the finish; even on the OUTSIDE of the casting where it had been chipped off. Its hard to peel off. I'd suspect with proper prep and in the proper places, since theres no mechanical abrasion...its not coming off
To the OP; I don't like rattle cans usually, but the duplicolor seems to work well for what it is.