Damage of that nature (on both sides) was caused by someone carelessly prying out that top gearcase seal and bearing housing assembly.
The water pump absolutely cannot function properly and will draw air.... either that area has to be repaired or the gearcase replaced.
DO NOT ever use silicone anywhere near a outboard engine (ugh!)... and JB Weld will not do that job successfully!
That area would have to be quite clean then you could have it heli arced (aluminum weld) and resurfaced at a machine shop... OR... by using a substance called "Marine-Tex-Gray" (not white), available at most reliable marine shops, dealerships, etc... and using masking tape as a wall to mold that area back into its proper shape (a little at a time)... after which it will harden to a strength greater then steel and you can then carefully (very carefully) file the top surface down to be exactly lever with the gearcase top surface.
One hellava job to do yourself... and time consuming. Best route would be the machine shop.
