Sorry for delay. We have been fighting weather down the Chesapeake and Alligator River on our way south.
We used GE SilPruf Silicone SCS2000 Series Sealant.
May be hard to find in marine stores. I got it at a general contracting supply. Information sheet is available from GE.
We are very pleased with the ports we have replaced. 3 to go. Waiting until Florida to finish.