I have a 1976 Evinrude 70hp model 70673d. I took it out and it ran fine we beached the boat and when we tried to start up to leave it was hydro locked. I pulled the center plug and the motor started right up but was blowing water out of the cylinder. I was able to limp it to the docks but need to fix this issue. In my research it seems it is one of 3 possibilities, bad reed valve, head gasket or the head it self.... any suggestions? Thank you in advance.