Wilma has only about 55K miles on her. 2008 Limited automatic. She would die after coming to a stop after being driven for awhile....then restart after sitting for awhile. We had a new Bosch CPS installed + the cocky young mechanic also attempted to re-solder the RCM.
The mechanic has had it for 3 weeks & is giving up. We're going to have it towed to another import shop as although it was driven 35 miles to this mechanic it will no longer start.

What's the next most likely failure / fix?

 

It may be possible that the fuel pump relay in your RCM may have gone bad. You can replace the RCM yourself. It takes 5 minutes. They are available on amazon, partsgeek, autohausAZ, etc.
When you replace the RCM send the original to @tighed1 to be rebuilt.He rebuilds them for very low cost and they are better than the new ones! You should carry a spare RCM and a spare crankshaft position sensor (BOSCH ONLY) in your car.
Here is a post I did on how to replace the RCM. It includes the proper part number. I hope this is helpful.
RCM replacement

 

That would be my next step as well.

 

Thanks for the reply / ies!!!

 

Also, only take it to mechanics that know Mercedes. You have a 2003 Mercedes SLK320.