I would use a very good RTV sealant for that.
One of the best ones out there in my opinion is "The Right Stuff" from Permatex.
This is the consumer version of the original Loctite 5900.
It is what is used for sealing the closure plate on Kohler engines. It sets up in about 1-2 min and you can assemble the parts immediately. It is advertised that it can be put in service right after assembly too.
I used it on my Kohler closure plate repair recently and so far it is holding up fine.