Deck stepped mast leak.

[Brion Toss]

Hello,
You can put a standup tube ó preferably with a curved neck, to discourage water intrusion ó either inside or outside the mast. The former will be easier for you, as you won't need to drill a hole in the deck (though you will need to pick the mast). The latter allows for ready access to the wiring, for inspection, maintenance, and upgrades, though it can be a trip hazard. And I've know of some boats that had a stray line rip the wires out. Oh, and the external version is much easier to step, as you deal with the wires after the mast is in; just yesterday we were fussing at stuffing wires down a little-bitty hole in the mast step, with the Mast of Damocles hanging uncomfortably close to our hands.
My inclination in your case, since you already have a hole, with wiring routed, is to add a generously large internal gooseneck, with messenger rove to pull the wiring in from below, and cut an access port in the mast wall, near deck level. You'll need to fabricate a hatch that screws on to the mast, and this can be done from a bit of mast of the same section. Be sure to drill and tap for machine screws. A hole at this level is not much of a concern even if left open, but a properly covered hole should actually be stronger than the mast.
Fair leads,
Brion Toss