exterior mirror assembly cover?
 

The right side exterior mirror assembly has a plastic shell on its front. That plastic shell is now broken. I expect, though, that the rest of the mirror assembly is intact and still operable. If it is, then I do not need to replace the whole assembly. But the plastic cover does need to be replaced, because rain will go right into the assembly. Is it possible to buy just that plastic shell and attach it to the assembly, without having to buy a whole new mirror assembly?

Depending on damage to the main assembily & mounting points, you can buy just the painted cap.

I had mirror damage before i bought the car, drivers mirror doesn't function on the electric switch but passenger mirror does so i don't think its the switch, more likely mirror itself. if you take yours apart and find any faults please upload pics and update thread. if i fix mine i'll upload/update here