I recently converted to R34 because I couldn't find anyone who would sell me the R12. I would take your car to a service place to do the conversion (take it to a trusted mechanic). These are old delicate systems and mechanics can make sure that the pressure and everything is right. Also, the receiver/dryer needs to be changed. Good luck.

Alex

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside