Bob,
The British parts diagrams show "grub" (set) screws into the four small tapped holes at the top of each cylinder housing, (the holes for the tank brackets, etc.). No one here has ever mentioned them in "roids", (my P/S didn't have them), but it might be worth a check. They must have been meant to "hold" the cylinder in place for routine maintenance like "de- coke". If nothing else, you might be able to get a little more "Kroil" in there if they are drilled thru.
Kevin