I guess the hole for the T fitting is fairly large (it is for the hounds) and silicone may not be able to take the water pressure without additional support. This area of the mast will dip 2 or 3 feet below water even fully sealed. So there will be some pressure.
Might work, might not.
Or you could buy a $5 tube of silicon goo, squeeze it into the T fittings, put some tape over it, and be done in 5 minutes.
