[Decolliber]

I need to get some R12 added to my system for the summer. The person who has done it in the past had Porsche experience, but has disappeared. I am wondering if I can just go to any auto a/c shop that has R12, or should I look for a place that has Porsche experience. Last time I called a local a/c place, picked from yellow pages, the guy tried to persuade me that he would have to convert the system to R134. I nearly fell for it.
I recall some postings a long time ago from an Atlanta Pelican who was also in the a/c business. I think he said there were some special techniques to recharging a 911, like making sure you keep the engine lid closed while recharging (damage to compressor otherwise?).