There is no real reason to seal them. They should have a drip leg so most of the water runs off outside the mast, but any water than does follow the wire into the mast runs down and accumulates in a purpose-designed box under the mast in the head, and then drips on the floor of the head, and out the shower drain. There is a similar arrangement under the mizzen mast, but that box drains into the engine room. At least that's the setup on our boat, SM#160.
This system of managing water that gets into the mast is much better than assuming you can completely eliminate any water intrusion into the wire chase in the mast, which is practically impossible.
The wires should all have a low point drip loop in the drain box, and you should check the outlet of the drain box periodically to be sure it is not plugged up. If it overflows, it soaks the bulkhead, and you really, really, REALLY don't want a water damaged bulkhead. Somehow seeds eaten by birds end up there, and the pits of some palm fruits and wild cherries are the perfect size to plug the drain!