Comptip and Mast Sealing

I am in the process of making my mast as watertight as possible per the many suggestions found on this forum. I got as far as the main halyard pulleys on the top of the mast and noticed that the foam in the top of the mast was a bit waterlogged. Questions: 1. Does this foam fill the entire comptip? 2. Is there a separation between the aluminum part of the mast and the comptip making two separate chambers? 3. I am planning on cutting a piece of stiff plastic or aluminum to the rough shape of the comptip profile and goop it in place at the top of the mast with 5200 sealant. Does sound like a good idea or is there a better way to seal the top of the mast?

Thanks for any help,
Matt