So a couple days ago my 2006 cobalt wouldn't start after a seamless 2 hour trip to Seattle and back. I check the fuel rail for fuel, and went on to the spark plugs. One of them had a wierd mark, I looked in the cylinder and saw a valve sitting on the piston. The other cylinders and valves aren't sitting wierd and she ran until I turned it off so I really don't think she jumped timing or scratched cylinder walls, just a broken valve keeper or something. With 240k miles on the car what would be a reasonable fix, if there is one?