Thanks Brenda (or David?)
I'd seen the CF post you linked to before but discounted it as it was discussing self tailers. Reading it again though and the following jumps out:
"To fully dismantle it is necessary to remove the winch
from the boat
(a real pain) because the pin retaining the bottom drive cog comes out downwards."
Could be the same for my winches and explain why I couldn't find it. Will be on the boat
tomorrow to check.