Hey there,
Darn it - I also knocked my mirror off! Like you, I'd rather replace the small part inside instead of forking over $500 to Lexus for a new mirror. Did you end up replacing your whole mirror? I was thinking of purchasing a scrap mirror so I can take out the plastic part but I'm not sure if it pops out easily or if it's glued in. Any advice you can offer would be great. Thanks!