Up here in Canada we don't have r12 available. I'm running an HC refrigerant in an r12 car (not my Benz) and have had no problems. I have found a source for r12 for my Benz and will run that as long as I can. When, not if my source dries up I will switch to HC and not convert to 134. At that time I will add straight to the r12 since none of the r12 up here is re-used anyway.

Jorg