leaking thermostat cover 1989 200 HP Yamaha

[rmastroleo]

I have tried everything. New gasket, the best sealer gasket maker(JB WELD) and still leaking. Now I have broken off a bolt following directions making a half turn more after an hour of the silicone setting. I am baffled. I can't understand why the water is still coming out. Can anyone offer any suggestions? TY

[panasonic]

Is the thermostat cover or the sealing face on the block corroded? Can you post a picture of it?

[99yam40]

corrosion hole in housing

[rodbolt17]

housing tend to crack.
sometimes all by themselves.