Corroded thermostat area on merc

[BRIELLY]

I changed out my t-stats the other day on my merc 135 and noticed there was some bad corrosion on the cylinder head where the t-stat cover meets the head. Sure enough its leaking some water while running. I tried some high temp silicone which is drying at the moment. I'm not sure if this will work or not. Is there a better fix? I thought maybe some high temp jb weld to build up the small area thats corroded but I'm not sure if it will last. Any ideas would be appreciated.