I've used duracool on several R12 cars thus far. As long as your system still holds some pressure, you can just dump the duracool on top of the R12. The duracool comes in R134 style cans so you'll need an R134 style low side adapter and R134 hose, preferably with pressure gauge. Be careful with the low side adapter. There are 2 styles. One is designed to work with the existing R12 shrader valve in place, the other you have to remove the shrader valve. Most auto parts places won't know what you're talking about but if you look at the bottom of the valve, make sure it doesn't have a needle that would stick into the existing valve. You don't want to have to remove the existing valve. Its messy.