I had mine apart to convert it to an air compressor after I replaced the head. It was leaky and low on r12 anyway. I noticed most of the o-rings were shot. I think it'd be a good idea to replace all the o-rings. There's one at every joint in the system as far as I can tell. You *should* replace the filter/dryer with a new one since it's been exposed to air/moisture. You can still get r12, it just costs a lot. Maybe you can get a deal if you know somebody in refrigeration. I'm told it works a lot better than the replacement, r134a. Of course you'll have to pressure test, evacuate it, and weigh in the refrigerant. I guess you're going to have a shop do that. Just my first thoughts. Good luck. I'd like to see how it works out. One day I'd like to get mine working again.