My 1985 300D is starting to leak 134A from the compressor manifold hose fitting at the bottom of the engine. I would like to "reverse convert" it back to freon during this repair. I do have freon based a/c experience and have all the tools except a vacuum pump. My question is what is the best way to get all of the ester oil out of the r4 compressor. Everything else can be replaced or THOROUGLY