Alright, as not everyone can access the group I'll share what I've done about replacing the delrin cup here too
I tried two different methods of replacing it, one using part of a juice bottle cap and one using part of a plastic "snap in" plug of the same size. Both work well... most hardware stores have the plastic bit, and the two metal pieces you are going to need, for about $1 total.
From left to right that is the factory delrin piece, the intact plastic snap grommet thingy and a modified piece of a juice bottle cap:
The "lip" on any of the three is to isolate the bottom of the battery from the metal of the switch. A perfectly sized plastic washer would also work but I could not find any. The threads and or unthreaded part are just there to help hold the brass shaft centered while screwing on the button itself. They also help keep the "lip" part from getting lost when you unscrew it to replace a battery. Here you can see that "snap in" part as fitted to the switch housing. The juice cap fits the same way, with a little grinding:
I used a razor blade to cut off the bottom section since all we need is the top part, with the "lip". I DID clean it up some and had to trim off a plastic seam on the inside so the brass plunger would slide nicely but all in all it only took a few minutes with an exacto knife and it was done:
But then what about the "bottom" of that delrin cup? This is used to both give the spring something to push against as well as to hold the brass plunger "up" while engaging the locking mechanism. If you use just the plastic bit that I've shown the spring won't work and the turning the lock will just unscrew the entire switch assembly. I found this brass washer in the plumbing department and surprisingly there is a gap between the top of the lock and the base that it screws into just the right size for such a thing:
A snap ring under the washer also fits and keeps the switch from unscrewing completely apart when the lock is used:
Finished and works better than when it was new