G2F, I don't know the answer to your question, but I have painted all of my cladding screws and haven't had a problem with them at all.  My cladding screws weren't rusty, but I took each one out, scuffed it up, cleaned it well, shot it with some Rustoleum and then re-installed it. (I would post pictures, but it seems that I can't from my work computer)  Many others have done this same thing with their cladding screws too.  Many paint their screws the body color, but since my VX is an Ebony I chose to paint them an aluminum color so they would stand out.
				
			 
			
		 
			
				
			
				
			
			
				"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong, it usually turns out to be impossible to get at or repair."
-Douglas Adams, Mostly Harmless