[88carrera]

Hi,
Yes, I solved the problem completely by installing a set of (4) adjustable upper rear control arms. Following this, it was easily possible to get the alignment into specs. For the record, I bought the less expensive set of adjustable control arms that I found on EBay and they work just fine. I think I paid around $400 for the set. I installed them myself (very easy) and then had a good alignment shop set the suspension up to specs. No more excessive inner tread wear. I have tracked the car and it handles beautifully.
I would advise anyone who has experienced this problem on a 996 to take this approach to solving the tire wear problem. Over the life of the car, this "fix" easily will pay for itself in reduced premature tire replacements.
Good luck!