Sounds like the same story as far as going to a CJD dealer for the CRD - massively inflated price compared to aftermarket. I guess Daimler did teach them one thing, all too well.
Thing is though, at least with CJD dealers, they're so desperate to make sales, that if they quote you an inflated price, and you tell them "sorry, but I can order it on line for XXX", quite often they'll drop the BS and MATCH the reduced price you quoted them.