If it's just a regular gasket, use some gasket sealant. I think skidim has some gaskets that have some sort of sealant built in as well. But when I did mine, I recalled JimN saying "use airplane gasket sealant." So, I did. No leaks for the rest of the time I owned my boat.
Previous: 1993 Prostar 205
Red 1998 Ski Nautique, PCM GT40, 310 hp, , Acme 4 blade, Perfect Pass SG/Zbox.
Be kind. Have fun.