grey permatex works well here
The grey stuff takes longer than the blue or black to set, and is alot thicker.
AKA its great for using on this application, since it won't get squished out as easily.
To the OP,
If you end up using a sealant put it on the surface and let it sit for a few minutes, then tighten the bolts down 1/2 way and wait an hour or two, then tighten all the way.
That way the sealant doesn't get squished out from between the two surfaces to be sealed.
Trust me, it works.