New to the forum, need some advice. 2010 MKT,3.5 ecoboost, right at 90k. Missing bad on #3. Took it to dealer, they say leaking into crankcase. Oil standing on top of piston. Told me I need an engine. Quoted me $8700 bucks. Does this sound right? They couldn't tell what broke. The miss started on the way home from vacation on the highway just cruising along about 75 mph. Car has always had Mobil one motor oil.