R12 and R134 have different Molecules, the R12 is larger and when R134 is introduced it has smaller ones and leaks appear, they cannot be mixed, your being mis-lead, the only way to properly service A/C is to add dye, charge the system and find the leak and replace the o-ring or hose, hopefully not the compressor, then evacuate the system and charge to specified number of lbs, anything else is chasing your tail,

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Jerry

2004 SL500 Black 55K Miles
2002 s500 Black 90K Miles
1986 300E Gold 233K Miles
1966 Twin Cessna 320D
1989 Jeep Cherokee 233K Miles
1994 Ford Van E150 399K Miles