It is quite common for the pins on the top cap to snap off when attempting to remove the top rigging from this part. You can also find that the plastic gets worn by the wires over thime, so we now sell this as a spare/replacement part.

When you re-mount your top rigging, tap the top cap down into place with a soft mallet to secure the wires. If you have to remove the top cap, use a thin flat-headed screwdriver to carefully prise the pieces apart, lifting the edges evenly to reduce the strain on the mounting pins.