Always best to start with the basics. Take a compression test, and drain/inspect the gear lube. Remove both large flat head drain screws (one is hidden underneath the gearcase snout) and see what drains out. Do not remove that phillips head screw, or the shift linkage will fall apart inside the gearcase. Dark colored lube is OK, but milky colored lube spells trouble, as does raw water or not lube at all draining out. Feel free to post pictures of your engine with any questions or concerns you have.
