One slightly used "Transpo" voltage regulator with 400 miles on it for Boxster and others in perfect working condition.
My original voltage regulator went out a few months back, and I replaced it with this aftermarket unit from a trusted ebay dealer. The alternator tested out fine and the voltage regulator worked flawlessly, but I ended up getting the whole alternator rebuilt just 400 miles later, due to worn alternator slip rings. Since the rebuild includes a new voltage regulator, I ended up with a slightly used voltage regulator that I no longer need.
I have a 2000 Boxster S, but this fits the Bosch alternator used in several other models and makes. Excellent info here:
http://986forum.com/forums/performance-technical-chat/21209-electrical-help-needed-post214414.html
Part number:
Transpo-CN
IB225-1339-12V
I paid $40. First $20 plus shipping takes it.