While I haven't simply just smacked the RCM (Mercedes part #A170545030505), I did buy a new one, and installed it last week to no avail. I've tried starting it with the following permutations:
1) old battery/old RCM
2) old battery/new RCM
3) new battery/old RCM
4) new battery/new RCM

none of them have worked.

any other ideas?