well not really leaking but seeps,I replaced last week with 1 from snyders,checked for square also head was true,used the thick copper gasket,torqued several passes over several days torque is at 55 lbs now water only no anti freeze yet,is there a stop leak that might work
I usually spray the copper gasket with copper gasket spray before installing it. I would stay away from stop leak and fix it right. Also make sure it's not trickeling down from the upper hose clamp.
Where exactly does it leak? I worked on a 1930 that wouldn't quit leaking until I removed the top hose and used my Dremel to grind the parting line smooth. It was just too much of a step at the parting line to seal up.