I have come a few times with my MB ML 350 Blutec, and repairs have been done in a quality way.
German Car Specialist have directly interfaced with my Lubrico Extended Warranty, putting in the claims for me, and then charging me the difference for what was not covered.
A minor item, is that they charge a labour fee to add in the Ad Blue diesel additive for the exhaust. Given that putting the additive in is a simple as fuelling your vehicle, and takes only a couple of minutes, I'd recommend that they drop charging this fee. My prior garage did this as a courtesy, only charging for the additive.