Manual air slide valve
John Schrampfer here. Would you do me a favor? If you are through with that valve, would you post on the MBShop site about its availability? Someone emailed me the day after I shipped it to you asking if I still had it. I didn't save the message. Maybe it will help someone else out in their diagnosis as well.
Glad to know you found the culprit. Now get that car running right and enjoy driving it for a change.