Fab, I bring the car to Randolph Racing in Stoughton, MA
.  They only work on Porsches, and I believe most of their business is done rebuilding them to be stricty track cars.  Their website is 
http://www.ranrace.com/
Kevin is the guy who owns it, they do good work, and are cheaper then the dealership.  
I originally brought it to Mays Tire in Easton, MA, they never fixed the problem.