Regardless of whether you choose greased or oiled, the Ester R-12 or PAG R-134a oil is not compatible with either, so it’s necessary to clean the compressor internals, which means pulling them apart. Pay attention to the condition of the oil when you open it. If it’s black and smells burned, the compressor isn’t worth using. Sanden compressors use five or seven little pistons mounted on a “wobble” or “thrash” plate. The main drive of the compressor has a plate mounted at a 30-degree angle in relation to the axis of rotation, which forces the thrash plate to plunge and rise as it rotates, making the little pistons go up and down. If you are very careful with the gaskets, they can be removed and reused.