Help with NON-Comptip mast head leak and sealing

I am working to get my mast sealed up as it caused me issues last season. I used a shop vac to put some presure inside the mast and discovered that the leak was coming from the top, or head of the mast. So I drilled out the rivets and pulled the head. What I found was a loose piece of silicon and under that a foam block. How should I go about resealing this old mast top before I put the head back on?

I cleaned the area as best as I could with a razor blade/file, then I filled the it with some foam (dont use greatstuff, I bought my stuff from west marine). After I put a little foam in there the little metal plate fit nicely sitting on top of the foam and I sealed it in with some 3M 5200. Reattach the mast head with 2x 3/16 rivets and youre good to go!