Most stud failures, from what I understand and have experienced, are the lower dilivar studs. The material used in them is not well suited for the intended use. (This is a subject of great debate.)
I have found that one of the best parts of owning a 911 is working on it myself. It is great satisfaction to pull the motor (easy) and do a top end or complete rebuild. These motors are not hard to work on. There are a few special tools required, but nothing that will break the bank. These are air cooled motors with individual cylinders and heads and a common cam shaft; just like motorcycles of old. If you rebuild it to stock there is no guessing at tuning or whether or not a combination will work, making the repairs even easier. A broken stud will take you a couple of weekends in the garage. If it were mine I'd re-ring it, have the exhaust guides replaced and get a valve grind. Other than new studs, that would be it, unless something shows up during the tear-down.
This web site is your single most valuable tool.
Lindy
