When you tested for vacuum at the switch over valve did you also notice the vacuum was gone when the air pump stopped running? The solenoid should close and thus you should no longer be pulling a vacuum though the small vacuum line at the switch over valves. If the vacuum is indeed gone then the solenoid is working properly; Opening and closing. One other thing that could be tested easily is the air pump output. The output air pressure hose from the air pump runs to a metal tube which runs up the front of the engine to the switch over valves. Un-clamp the spring loaded clamp and pull the rubber hose off the metal tubing. When you start the cold car the air pump comes on and you should feel the air coming out that hose. It is a large volume of air and easily detected. JUST BE VERY CAREFUL OF THE SPINNING BELT!

After testing the air pump discharge you have completed all the physical test to the system with the exception of the switch over valves: The vacuum lines have been tested and proven to show vacuum as the solenoid opens and closes. The electrical circuits are all working properly or the air pump and solenoid would not be working as you have tested. SO the only thing left is the switch over valves. I know you have said the originals have been removed and a set of used valves were installed. Did you inspect those valves for cleanliness? Did you apply a vacuum to them to see if the diaphragm was good? Where the valve bolts to the car was the passage open and clean? Did you use a new gasket ? I have seen pictures where the passage at the block was completely clogged and thus no air could get into the exhaust. If you clean these try to use a good vacuum cleaner with a long tube fitting so as you clean the passage you are sucking the dirt up and out and not allowing it to fall into the exhaust chambers.

PS did you send your old RCM to Tighed 1 for repairs?? He lives in AZ as do you and he has repaired hundreds of RCM for us. Send him an email tighed1@hotmail.com It will be better than new and you will have a replacement should the need arise in the future. Most of us carry a spare RCM and CPS with us in the glove box at all times.

With your scan tool have you cleared the P0410 code?? It won't clear by itself. As you said above you repaired a vacuum leak, so maybe the problem is corrected.

Thing is P0410 is a generic OBD II code. Mercedes also has codes P2003, P2028 and P2029 which breaks the problem into separate factors which helps to further diagnosis this problem. Not sure if they even apply to Crossfires. You need a good scan tool that can get into the Mercedes codes.

After all that is completed I really don't know what else to do other than watch the lambda and glean what info you can from them. You said you can't find any other DTC through out the entire car's other systems, so I'm reluctant to suggest other testing as we would really be getting out into the weeds.