I just rebuilt my compressor last week and it will require evacuation. Doing it on the car would be difficult with all the snap rings involved. Mine was leaking from the ports so I took it off the car and discovered more oil leakage from the front where the shaft seal is so I decided to replace all the seals. What kind of compressor is it? If its a nippondenso like mine there is a good writeup at www.pelicanparts.com/techarticles/911_Nippondenso_rebuild/911_Nippondenso_rebuild.htm. Took me about 45 minutes to rebuild with a kit from acsource.com. Works like a champ now with no leaks