If you read through all the previous threads on Mistery No Start and Relay Control Module, there are quite a few, I know !!! Try to relate some of the symptoms previously mentioned to the symptoms you are experiencing with your car. That may help your diagnosis.
For instance, mine would start cold and only times when it was hot. When not starting hot and the key was turned to the "ON" position, I didn't hear the fuel pump start up and prime the system as was always normal. Or you could wait till you have a "No Start" condition and "tap" the side of the Relay Control Module containment and see if it starts then.
I hope some of this helps, it can get frustrating as HELL to attempt to trace down minor electrical mishaps !!!
BTW: if it does turn out that the CRM is bad, your local Mercedes dealer should have the part in stock and alot cheaper than if you went thru Chrysler !

Just my Dos Centavos