I have had a number of Merriman
winches in my life. They made quite a number of different styles. They did make one model with a circlip outside the
winch handle socket which you apparently do not have. I had one model with a big bolt with a giant screwdriver slot that was at the bottom of the
winch handle socket. I had a reel
winch that you had to unbolt a frame at the base of the
winch and then there was a bolt on the bottom of the
winch.
Jeff