Check them out at ripoffreport.com. Just look up gbox and see my story with them
http://www.ripoffreport.com/r/GBOX-Porsche-Gearbox-specialists/Boulder-Colorado-80803/GBOX-Porsche-Gearbox-specialists-5757-Arapahoe-Ave-lied-about-repairs-put-used-parts-935100
This wasn't even a case of poor workmanship but misrepresentation and fraud. I wouldn't recommend them