Was the car originally r12? If it were not then it is probably designed to do a good job on r134. If it is not performing up to spec on r134 then it may be something not quite right with your a/c. On the other hand if it were r12 originally I would definitely go with r12. I'd have to look up in the manual what it says about that particular compressor in regards to being able to flush it out. If no one comes along and gives you a definite answer pretty soon I will read up on it and let you know.