Winch base repair and reef line attachment

[Brion Toss]

Oy,
As Ian indicates, the failed winch might be a particularly loud canary in the coal mine. In addition to all other winches, I'd strongly recommend you get a complete rig survey; even if you don't have electrolysis compromising everthing else, simple age and use might have brought the rig to a dangerous place. Please see to this soon.
The repair will indeed require a separate plate, with the winch tapped to that. It might be possible to use existing holes, with larger fasteners, to attach to the mast. But you might also be able to make an extra-large plate, with fasteners well outboard of the existing holes. And I mean well outboard, so you don't get into a "tear along the dotted line" situation.
And contrary to what Ian says, you might want to use the reef winch, just because it's easier. But try marking the clewline, for a do-not-exceed point.
Fair leads,
Brion Toss