My car has been with a mechanic for a few weeks. When it first was taken apart, the apparent problem was one cam shaft (intake side?) was badly worn, while the other was ok. It also ended up that the Rocker arms on that side were badly worn too, allowing these little shims, that sit below the rockers to space them correctly, to simply fall off. One of them fell off and it caused a valve to bend in and dent the hell out of the cylinder head/cylinder. I think it was the number 3 cylinder for reference. The mechanic should be finishing pretty soon, but i have to tell you, for a "bullet proof" engine, this scared the hell out of me. About $1,400 in parts, and a little over $2,000 in labor. 4 months out of warranty, lol.