I saw a post here that has a great picture of the bulb out control module...so I pulled mine to see if there was a problem with a connection. Well there sure is!!
As soon as I removed it I heard a rattle in it. There is a major burn out between two big flat modules (nice description right?). While there are many small connections and some chips on the boards, there are a few (4?) flat metal plates that seem to play and important role. One of mine has burnt to a crisp and does not serve its purpose. a piece of the connector was loose in the module.
enough of that. my questions:

• what all does this module do?
  i have a faulty (not working) RR side marker. could this cause it?
  what are my options? would a used module from Sun Valley Mercedes Dismantlers be a good option? ($75 vs 240 dealer)
  what would cause such a failure? will my new/used replacement burn too?
  What can i check to make sure i don't burn the new one?

thank you for any info...and yes my license plate lights work!

No - but on the board it attaches to says 'S15' right where it is soldered on the board. I tried to snap a picture but it is hard to get a good close up that shows the burnt section. I'll try to attach one here...
Thanks!
John