2011 MERCEDES-BENZ GL450 Engine Problems

Check Engine Light came on and took it to the mechanic who identified low compression on cylinder #3. The injector was replaced which did not fix the issue since the vehicle lags when first accelerating. We were also informed of a service bulletin that included the issue with our vehicle and to take the car to the dealer. The vehicle was taken to the dealer who did not check the cylinder low compression/leakage issue because the check engine light wasn't on, which it would not be since it was recently serviced, and the number of miles required had not been driven for the check engine light to come back on. Even though the service bulletin is for the same make, model and years because our VIN was not included that there is no warranty on this vehicle. I now have a vehicle with an engine issue that should be included...