I belong to a group on Tribe called Porsche-philes. The first guy to respond to my inquires about buying a used 911 was Shamus. He was really very supportive and had a number of books to recommend, steps to follow and things to watch out for. Shortly after my post, he purchased a 1977 911. I recently followed up with him to see how the experience went. I've quoted a few relevant passages below.
". . . the rear sway bar mount was cracked (a common problem) and the shocks in the rear had to be replaced. My mechanic recommends flushing the brakes every three years, so I had that done. The battery was the wrong size, and badly jury rigged into the compartment, so I just replaced the battery rather than weld a clamp for it. . . "
". . . After a couple of months, I noticed that every time I used my turn signal with the lights on, the highbeams would come on. Again, it's a common problem because of the way the headlights are wired. $300 for that. I've also discovered that the cigarette lighter doesn't work, which is a problem, in that the spare tire inflates with a little pump that plugs into the cigarette lighter. It wasn't the fuse, so that's something for taking it back to the shop. . . ."
". . . The biggest annoyance is that there's a leak, and it rains a lot here. . . while I consider whether I spend a grand to replace all the seals . . ."
". . . The pop off valve ended up being the big story for me last year. I was getting some stalling upon deceleration, you know, just cruising up to a stop sign. The guys at the mechanics just said that it could be a hundred things, and you might just have to put up with that. Then one day, it just didn't start. After consulting with Pelican Parts, they said that likely it was the pop off valve. Sure enough, it had popped out, and taking apart the air box and popping it back in got the car running. But then I ended up having it pop out on me at a stop light, and later on the interstate, and I had to do roadside or middle of the road repairs. That was no fun, but at least it first broke down in my parking spot, and I was able to know what it was and how to fix it. Once the valve was replaced, the stalling on deceleration went away. I guess it was just leaking before it popped out. . ."
Ah, the joys of classic car ownership! I have great things to look forward to.