Hello,
You could try the nearest dealer or the supplying dealer if you are the original owner to see if it will be a *good faith* or *secret warranty* repair. Failing that, use an indie to have the work done ASAP, rather than be towed in and then have it done *under duress*.
I think that MBUSA should be doing all these for free, the E320 was an expensive car to buy when new and this kind of failures are unheard of on the Mercedes that I have owned and/or driven for years.
Hope that is of some help, I am too far away(8604miles)to volunteer to do the repair for you!!

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Nachi11744