"C sensor" Coolant temp sensor? Right next to the thermostat on the lower intake manifold. I didn't watch the vids but I've changed these gaskets a lot in my car and its super important to torque the LIM bolts perfectly or it WILL leak causing the lean condition. Take your oil cap off and feel if there is any positive pressure or a strong vacuum. If there is a strong vacuum in the crank case then its defiantly leaking. No silicon should be on the intake or coolant runners. The silicone is important were the head and the valve cover meet but not as much as the bolts. Invest in a inch pound torque wrench. Too tight and the gasket will leak and probably crack the middle intake runners so be careful. (All of this from personal experience and help from the awesome people on this forum)
