I have taken apart a different model Kurt but they probably have the same retaining clip on the screw. Look where the hex end comes out of the base casting there is a retainer clip there. It is not like a regular circlip with little tabs and holes it is like a multi turn flat spring. You should be able to see a little concave arc on the inner corner of the end of the spring and you can get under this with a tiny screwdriver and pry it up then work another screwdriver between the part of the ring that is above the groove and use the two screwdrivers to work it out all the way around. It is fiddling and you have to be careful not to strain the ring too much in any single location because it will bend or break.