In regards to the "discretionary" fund, this is referred to in the dealer environment as "DSA", Dealer Self Authorization. It actually is MB's money, they allocate a certain amount, depending on the size of the dealer and so-forth, for the dealer to use on out of warranty vehicles. DSA is commonly referred to as "Good Will Warranty, Customer Good Will, etc.
Most dealers will reserve this to help out their better customers, that is, people who buy cars at that dealership and/or frequent the service department. Makes good sense to utilize it in this manner.
I would first have a VMI run on the vehicle to see first of all if the car has an outstanding recall campaign that perhaps pertains to the EGR valve, it seems to me there is a actual campaign for the EGR valve on this car, and if it outstanding (ain't been done yet) then there is no question they will check it out and replace it if neccesary, free of charge.
In regards to Steve's last paragraph, I was never an "MB employee", just a dealer tech, and I may as well say it right here, I'm not there (at Zimbricks) any longer, been gone since April, but I'm still happy to help out here at MercedesShop. Not wrenching at all right now. (This is why I changed my user name to "Gilly" rather than "Gillybenztech")