My 2006 Chevy Monte Carlo SS 5.3L had check engine light June 16th. Made a quick stop and the car wouldn't start. Turn the key again and it started. Stopped at a Advance Auto Parts and put a scanner on it and got a P0335 code(Crankshaft Sensor). The next day I took it to a shop for repair, and they informed me that two of my manifold bolts are missing. It could be the heads are broken off or they are actually missing. So they didn't want to repair it. My question is if the bolts are broken of in the block, can they be removed? The car runs well so far owned it for 3 years. Need help and advice.