This might be a good time to go ahead with a conversion to 134. I did it in my old BMW 735i and it wasn't that expensive, maybe $600. The indy even had to do some special "plumbing" on that car. Considering what you may be looking at to repair and recharge with R12, you may be at about the same cost.
Oh yeah, the R134 is not as cold as R12.
That will be $0.02.