Yesterday I went to an excellent boat supply shop, Whitworth's, and was able to source nice pulleys and nylon cord that's the right size for it so it won't slip off the track and jam.
I was talking knots with Rob VK2ATC on 20m and he mentioned the bowline which is an excellent knot. (I've been using a round turn with two half hitches).
Whitworth's, and no doubt other boating suppliers, had other useful things such as self-amalgamating tape (you stretch it, then wrap on itself, and it bonds to itself making a water tight seal), heat shrink tubing, and all sorts of useful stainless steel fittings.
Although there's expensive stuff in there, the pulleys and cord were cheaper than the rubbish I've been using.