Rust bubble....how bad could this be?
 

http://i.imgur.com/XkM11Ex.jpg

I am looking at a 80s 911 that looks to be in overall good shape but has this. The story, as told by the current owner, is this. He had the car painted about 20 years ago. While doing a glass out respray the bodyman had trouble reinstalling the rear glass. A few years later this little jewel of a spot shows up. I know the glass would have to come back out for any kind of repair. My question is how bad could that spot really be assuming it is the only rust issue the car has.

I doubt that it is terrible (rust through) but it is certainly to address.

Bad prep after the glass was removed. Not too concerning. Just hope there isn't a hole to the interior.