I'm assuming you've obtained the DuraCool. It's sounds as though you do not have a 609 certification(what you need to buy R-12).
Assuming I'm right, how did you obtain the DuraCooL?
I suppose my point is, if you obtained DuraCool w/o a 609 certification, then DuraCool is not a true R-12 replacement.
Many people buy these "alternate" refrigerants" thinking they are true R-12 replacements. Freeze-12 for example is 80% R-134A, yet costs almost 3 times more than R-134A.
I'm not trying to start another refrigerant war, just wish to say that these "alternative" refrigerants are not always what they are cracked up to be.
The 609 test is only $20-$25. When I took it, the thing was open book with a total of 25 questions. Kinda like taking a drivers license test or in other words, any idiot can pass it.
Get your 609 cert. and buy the REAL thing. The cost of R-12 is far less than trying to swap out systems.
Just my 2 cents.