The dealer uses a syringe type device to insert some oil into a screw in port in the compressor. Car parts shops sell ester oil in either a 2 ounce can or an 8 ounce can mixed with some refrigerant for pressure to force it into the system. The syringe method would be the preferred method because you can just inject it until it doesn't make noise anymore, but whether you could get your hands on one of those devices cheap I don't really know. I'm also not sure that ester oil is the correct oil. I talked to a mechanic at a dealership and he told me thats what they use but I'm still skeptical that the correct oil.