John, my advice would be to do an overhaul while the system is empty. Replace the o rings, replace the receiver drier, and replace the expansion valve. When you have everything apart you can clean up the condenser and check for bent fins. At this time you can either choose to remove the compressor and empty out the oil or you can button everything back up once the system has been overhauled and flush everything out and add the new oil.

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1990 190E 3.0L