I'm happy with my Delco R4 compressor I installed a few months ago. You can get one for $240, it has a shorter clutch so it will be further away from the oil cooler lines, and it runs smoother than the aftermarket factory air compressor that was on my car. I am using r12 now, though. Didn't have a problem with stepped ports or anything either.

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1980 240d
1999 SL500