Larry and Jeff are quite correct in that if you are using R-12 refrigerant, you must stick with the mineral oil, 525 viscosity. It is a special refrigerant oil, as you thought, and is available at any refrigerant supplier. Since you are replacing the compressor, I made the (incorrect?) assumption that it had failed from an R134 conversion, as they will all do, if the correct oil isn't used. Sorry about that! If you do switch to R-134, the system should be flushed as completely as possible, and the correct oil used as mentioned in my earlier post, to prevent premature compressor failure.