Graham,
I too have the Z-Spars furling gear and I had it apart recently. It uses a plastic stopper that clamps to the forestay wire to stop the PVC sleeve from dropping down onto the lower terminal. Perhaps yours is loose or missing?
Also, there is a cap-head screw that passes through the top of the furling drum and into the internal alloy sleave. As well as securing the drum, from memory, I think that might also help to clamp the PVC sleeve. Mine had the wrong length screw fitted, which meant it wouldn't tighten properly. The manual specifies 12mm (M6).
My mast was down when I disassembled my furler but it doesn't have to be - assuming your forestay set-up is the same. After the cap-head screw and the bolt below the drum are removed, the drum has to be rotated because it can only be raised in one position, when it's aligned with the plastic stopper inside (assuming you have a stopper!).
Hope that helps. If you don't have the manual, I can scan it and e-mail it for you.
Anthony Russell
235/02 Sea Wyche
Anthony Russell
235/02 Sea Wyche