Seems all to common. When I got my '71 Mach 1 in 08, got it home to SW Ontario and was able to give it a really good 'once over', it became obvious that at some point in it's life, someone had backed it into something hard............. and on the right corner! The bumper was a repop for starters. The car had been repainted by a PO and I got the story on how and why it was done, so the damage had to have been done prior to that and repaired. Only when I had the car stripped and redone, did we find the extent of the damage, but fortunately not too bad, just needed to replace the rear light panel which had the obligatory rust pin-holes in it anyway.
As for mirrors, no doubt you've read posts from me about an enlarged convex mirror I made for my car. The ones currently on the market make rear vision worse if anything. Even with my mirror, I am thinking about adding a full time rear view camera, but where do I "hide" the camera? I have an original license plate surround from the dealership and I don't want to mess it up or lose it. My thought is to go with wireless type and bypass the back-up switch. I need the largest screen available and I need it to be removable so it's not seen when at car shows. I did like the one that goes on the rear view mirror, but a bit too small for my old eyes. Still a maybe!
Yes it sucks when we hit "stuff". I took the paint off my right front fender while backing out of my 1 car garage, trying to NOT back into something!! (Hence the need for the repaint in 2013)
Geoff.
mustangs have their own character 
