Having worked on the "wholesale" side of the auto business in a past life, I would HIGHLY RECOMMEND you contact Mercedes N. America. You are exactly the customer they need to hear from.
I used to work for Porsche. I was in charge of a region. We had a lot of high profile customers: industry, entertainment and sports figures.
The inexperienced dealerships would often try to do a quick fix or solution with the customer caught in the middle. When these situations were forwarded to me I fought for the customer with some rather impressive results. People would like to label it as the squeaky wheel syndrome, but I would describe it as "at least meeting customer expectations, and hopefully exceeding them."
You may be able to recoup what you had to spend. Why? Because their authorized agent, to whom you took your car to in good faith, did not conduct and act in such a way that reasonably represented their brand.
This may sound like a lot of double-talk/corporate speak, but I am sure if you press it and not yield, you will be very please with the results. But you have to step forward.
If you need the customer relations contact info, email me and I would be glad to forward it to you.
On a technical side to all the discussion regarding cylinders awash with fuel, the first thing I would have done is pulled the dipstick and smelled the oil.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)