In the CAV-15 Receiver, the selector spring and detent load from the top and the selector is then slid over top of them. The selector does not need to be removed to service or install Mil-Spec Fire control parts.  In the case of some match trigger cassettes like those made by KE Arms, the selector does not need to be removed for installation either.

If you do need to remove the selector doing so can be tricky for inexperienced people.  If the spring is not trimmed appropriately, it can be difficult to impossible to remove the selector without breaking the inner wall.  In some cases the track and the detent locations in the selector are too deep, also making removal much more difficult.

This article assumes you have broken the inner wall of your CAV-15 receiver in removing the selector.  Repairing this to function  properly is fortunately very easy.

Broken inner wall with broken pieces removed.

Acquire metal tubing from your local hardware store.

Make sure the selector detent can fit inside of it.

Remove the rim from the bottom of the detent.

File the bottom of the detent flat.

Drill the selector hole out to the larger diameter required for the tubing. Friction fit is fine. Make sure not to drill the hole deeper. If you do you will need a longer tube that can house the spring and the detent and to plug the bottom of the tube.

Cut the tube to the length you need to reform the inner wall.

Tap the tube into place taking care not to deform it.

Another angle of the tube installed.

Spring and detent installed.  Note height of detent for properly trimmed spring.

Another angle of the spring and detent installed.

Operational again with KE Arms SLT-1 Trigger and Ambi Selector Installed.