c280 oil leaks, round 2 w/dealer

Just keeps gettin' better--now that the dealer has fixed? the oil leak at the head gasket (last week), it still has a steady leak. Upon the return visit, they say that now they've removed the pans, cleaned off the area and the rea seal is leaky. At 64k. After I just took the car in for "oil leaks", and they billed mercedes $1420 for the job(in fairness, they repaired all but $500 under goodwill warranty). How much is fair labor for leaky rear seal on these cars? I'd much rather my independent do it, who I trust, but I feel the MB store owes me a little responsibility. Who wouldn't clean up the pans to check for oil leaks, and how much labor would I have saved on just one job? Help! thanks.