Thanks MikeyGnz, Jaysen and Tom!
Your comments provoked me to try to better understand a sensible way of balancing protection from salt water corrosion and maintaining motor cooling. So I called long-established and respected Muir Winches, the manufacturer of my electric windlass.
Muir's advice was clear: prioritise safeguarding the electric motor and attached gearbox against saltwater corrosion, as heat build-up is not a significant issue, given the intermittent and short operating times of the winch and gearbox.
Muir recommended wrapping both the motor and gearbox in Denso petrolatum tape (Egyptian mummy style), while leaving the inlet and outlet openings of the air cooling fan's shroud unobstructed. See https://youtu.be/ZKOgAFKmneQ for a colourful (from what-part-of-America?) description.
This afternoon I applied a third coat of varnish to Great Sandy's helming seat and associated trims, brought back to Noosa just before Saturday's snap Delta Covid lockdown. For the time being, I'm Noosa, and unable to travel to Mooloolaba to work on Great Sandy.
The child bride and I are fortunate to be safe, healthy and happy though.
Currently building Jacques Mertens ST21 "Skinnydip". Boating adventures: Splash testing and using 'Skinnydip, as a basis of further building refinement; Adams 44’ sailing sloop "Great Sandy" (cruising and maintaining); Iain Oughtred Feather Pram "Mini Dip" (building); Jacques Mertens R13 "Wood Duck" (built and due for maintenance).