a few years back my mirror fell off. the body shop put it back on for me but then had a big blob of discoloration at bottom i never did anything about it . today i knocked it off while washing windows .now i discovered the blob moves around as you flip the mirror around. was going to go to the used parts outlet "aka" junkyard to buy another but wanted a little more info so when i got home w/ new one the same thing wouldnt happen anyone seen this and what is it it looks like oil