I converted the R-12 system of a 1990 740 to R-134 using the Volvo kit which included a bottle of ester oil. After various other problems including replacing the compressor, the system worked again until the condensor blew a leak. I took the car to a shop and they found the leak. They also told me that ester oil is not to be used with R-134 and now they want to flush the entire system out.(139.95) If this is true about Esther oil, then why would Volvo include it in a conversion kit? What are PAG and POE oils? Are they the right oil with R134? Should I disregard this and just put in the new condesor with a dose of ester oil to replace what was in the old one? Thanks for ending this confusion