My Mercury 850 from 74 is leaking water from a 3mm hole on the left side in the exhaust manifold cover. Can I repair it with JB Weld or should I replace the cover with a new one. From the parts catalog I can see that it is an plate inside the cover as well but when I put a small screw driver into the hole it goes 3 inches in.

Low pressure in there.. I think JB would be OK