the pump is probalby fine. the O-rings are avilable at napa . just remove the from all the hose and tube connections and bring them in and match them up. pretty standard stuff. I have done it on stuff from teh late fifties and had no problems. but get it evacuated first freon is not goo dstuff to breathe and it is expensive so if the system is still full it can be put back in after you replace the seals. But on the other hand if it is full then maybe just try to run it. but if youhave to take it apart to install in another truck then you have to have it evacuated first. if the system is empty then there is a 90% chance it is because the orings dried out and leaked the freon out. replace all orings and refill with 134A. done.