If you look up my post for the same question in the Tech help forum, MB Doc replied and recomended 6 oz for a completely flushed system. I have an 88 SL with a Denso compressor. I used Ester oil which is compatible with both R-12 and R-134. I charged it with R-134 for now so I can verify there are no leaks and no problems. I will be re-checking it shortly and if every thing is OK I will evacuate and recharge with the last of the R-12 I currently own.

John Roncallo