Was smelling some burning oil under hood so took my Stock 02 WRX with 170k to a so called Subaru specialist. Diagnosed to have leaky valve covers and cam seals.. had that done as well as the timing belt to save future labor costs. Got the car back and after driving 30 miles, the check engine light came on.. brought it back and they said it was due to the timing belt was off my one tooth.. they made the adjustment and sent me on my way. 5 miles down the road, another check engine light so i brought it back.. They then diagnosed a miss-fire on cylinder 4.. They could not attribute it to anything but perhaps something caused by the timing belt replacement and they would stand behind their work. They pulled the head and said they had found a burnt valve.. they said it was not something caused by what they had done, and it is going to be another $400 bucks... I had no check engine light when I brought it in and it was running great with no power loss etc... Is is a coincidence that I have a burnt valve or could it have been caused by the work they have done? Car is in the shop and need to call them back.. Any thoughts or ideas will be very helpful. THANKS!