Here is my second A/C thread. I have a 1984 240GL 4 Dr Sedan with a B23F engine, and every season I need to add R-12 refrigerant. I can't say exactly how much because I add from a 30 lb bottle. Yes, I do have a CFC license to do this legally. My initial question was answered by my previous post, that this is indeed normal for a vehicle of this age and that apparently there is a leak. But, I am unable to find it. I've tightened all accessible fittings and injected "Die" without any results. My second question is, would it be a good idea to upgrade to a R-134A system and what would I have to replace to do it?
R-12 is getting very difficult to acquire and the cost is totally ridiculous.

Thanks for always answering my questions in a professional manner,

Eric