Ran the ol' trusty Honda on the muffs today and noticed water leaking out of this hole! Guess it explains the rusty screw heads around it. Anyone know what would cause this or is it missing a screw there? Still runs great. Lol
I think that you have a water jacket cover that's perforated from corrosion. But do you have a model and serial number.
I took off the plastic cover and this rusty thing is what I found. Looked to be a thermostat. Is this the flush valve?
No, that is the thermostat.(it may be a good time to change it) The flush valve should be in the hole directly above it. Is there anything on the cover?
That explains why you had a leak.
I'm thinking like w2much. Drill, tap and plug the hole. You could tap for a bolt, file the surface flat and put a washer under the bolt head. Or use a pipe tap and put in a pipe plug. But don't over tighten the plug or you may split the boss.