Mercedes Benz C Class engine misfire

Problem started one cold morning when on starting engine a misfire occurred and it was lumpy on idle. Slight pressure on accelerator seemed to clear misfire and I drove the car for approx 5 miles. On returning home similar symptoms occured and I booked car in for diagnosis at dealership. On restarting to take the vehicle for its diagnosis the engine still misfired and had developed a slight rattling sound. I immediately stopped the engine and contacted Mercedes Mobilo Breakdown who very efficiently recovered the car to the dealership. The car has always had servicing at specified intervals and has completed 82,000 miles receiving its last service two months ago.

Unfortunately the diagnosis shows: oil level fine but STAR test shows several faults including knock sensor (PO325) left camshaft hall sensor (PO341) also misfiring of cylinder 1 (PO301) and cylinder 3 (PO303), suspecting possible timing chain fault. The dealership has quoted £1465.00 to remove the cylinder head to confirm exact problem, before anything else can be done!!!!!!

I maintain that a C-Class engine should not be developing this sort of problem at this milage considering a full service history since new. Has anyone else experienced this sort of engine problem?