Got a MB EGR valve from local shop for $89.10 (a STEAL!) and put it on last night. What I found on the old EGR valve was interesting. I could not get the EGR valve to open by pushing up on the diaphragm with my finger. I pried up on it and obviously broke loose the carbon seizing the shaft and it moves freely now. I left the new EGR on as it is nice to have a new part, but the old one will be kept as a spare. Had Autozone clear the P0400 - I drove it last night and wife has driven it a few times today and the code hasn't come back.