I just bought a Mercury Mark 20 and was wondering if anyone can help with some questions? The power head is not stuck. I can turn the flywheel back and forth but the motor will not turn over. I think the water pump is bad not allowing it to turn over. I have pulled the plugs and oiled the cylinders and removed the small side covers on the block allowing me to see the sides of the pistons and they look like New. The power head still has the factory seal so it has not been apart before. Any Ideas on what to check or problems any one has seen with the Mark 20? This is my first old Mercury.