Originally Posted by onehundred80

You can buy them on eBay quite cheap, I got one for $45, there are older models of them for other Mercedes and they are cheaper and work the same. Turbomar used one and had no problems, he lists the part number in his post on the subject. Basically the only thing that goes wrong with them are the relays and they can be fix quite cheaply.
If you have problems with a RCM check the fuses, poor soldering and look for burnt out contacts and windings on the relays.