If you're replacing a compressor I would advise using a reman unit from Mercedes to safeguard against problems later. That would also be the perfect time to switch to HFC-134A. If the conversion is done correctly you should have no problems with reliability. And yes, you may feel a temperature difference when the system is functioning in high temp and high humidity conditions the vent temp may be as much as 10 degrees higher.
ASE Master Technician, Lead Technician for Deutsch American Inc. Over 6 years of Import Service-specializing in German Automobiles.