There is no real need to purchase an a/c compressor from MB to ensure quality. This is a standard item from Nipondenso and can be purchased rebuilt or new for less money from many other sources with no fear of lower quality.
The best source I know as an alternate source for a/c compressors is via www.aircondition.com. There are several suppliers there including ackits.com.
The biggest concern you should have when replacing a compressor involves what exactly failed in the compressor necessitating its replacement. If it failed internally, it is necessary to THOROUGHLY flush the system to remove the debris that a failed compressor spreads throughout the system.
If the compressor is merely being replaced because the shaft seal began leaking, then it is a much less catastrophic situation and can be handled by simply replacing the filter drier, evacuating and charging.
Best of luck,