I would remove the compressor and drain the oil out of it and replace it with the correct amount of oil. You can still buy the correct compressor oil on Amazon when I last looked a few months ago. I keep a supply of oil that matches up to my supply of refrigerant. One is no good without the other. I would also replace all the "O" rings with new Viton "O" rings while you are doing the servicing. You should also replace the receiver / drier right before you are going to complete the servicing. I have done many an air conditioning service using R12, and I never install refrigerant into a system until I am absolutely certain that I have addressed every possibility of a leak. This means new O rings, cleaning of the evaporator coil on the outside, and cleaning the condenser also. If I am not certain of the system's condition, I also purge each component separately with a cleaning agent meant only for air conditioning. Once all this is done, I will draw a vacuum on the system, and I like to get it down to at least 750 microns and see that it will hold the vacuum for a minimum of 1 hour. Then I will charge the system with nitrogen to check for leaks under pressure. Only after I know that it holds pressure for at least an hour, I will evacuate the nitrogen, charge it with R12, and install about 85% of the total that the service manual specifies. At that point, I will start the car and run the system while watching the site glass for bubbles. I will add refrigerant in small amounts till there are no more bubbles in the sight glass. Usually, I will see a thread going across the site glass, but if I am getting good cooling inside the car, I just stop. I use a 30-pound cylinder of refrigerant and a refrigerant scale to know exactly how much I have installed. If you are using 12 or 14-ounce cans, you can keep track of the quantity by doing the math. I always install the metal caps, and this year I learned about a product that helps to stop leaks from the Schraeder valves. It is called " Nylog Blue ". You put a drop or two onto the threads of the metal service port cap and then screw it on hand tight. Then give it a slight tweak with your socket to seat it, and it will stop leaks from the service port valves. It only works with the metal caps.