I assume you are refering to the fact it is difficult to completely flush the condensor when it is a parallel system. True. I hope that after all these years the oil has made it's way to the bottom and a flush will remove most of it. It is the oil I am most intersted in removing. So far I have not seen any evendince of any major contaminents, or signs of black death.
I am always interested to hear that many people (including shops) have successfully converted from R-12 to R-134a simply by changning the drier/fittings, pulling a vaccuum and charging with refrigerant/oil.
'89 Spider Veloce