Almost a year ago, our fairly new shower valve started misbehaving. It would pop out and spin freely without affecting the water flow. We could make it work by pushing it in while turning, which was a "reasonable workaround". Therefore, I took way too long to get it fixed.
I finally took it apart a few months ago to get to the bottom of the situation, but quickly ran into what I thought might be a point of no return. And if I couldn't get it back together again, I'd be at the mercy of plumber emergency visit fees before I could turn the water back on in the house.
Later I had a plumber out doing some other work and I asked him to look at it. He was entirely unhelpful and just suggested that we call Kohler for advise. I find it hard to believe that a plumber who has surely seen countless shower valves in his life wouldn't have a hint as to what was wrong, but anyway...
Fast forward to this past weekend when I decided to go all-in on getting this fixed. I pressed on enough to remove the broken part, and after some searching around on the Internet, found that there was a single Kohler part that looked exactly like mine.
From there it was smooth sailing.
Pretty much all videos about broken shower valves that I could find are about are really basic and focused on the handle itself being stripped. This was not the issue here, so here's a video to help you fix your own shower valve rather than getting a plumber to shrug his shoulders at you or charge you way too much to fix it. Not sure which is worse.
The part that I used is Kohler GP77759 Kohler Mixer Cap Unit.
I bought it from Amazon. Ordered on Sunday night, had it in the shower on Tuesday.
While you are in there, you should also replace the shower balancing pressure unit: Kohler GP500520 Shower Pressure Balancing Unit.
I did not do this in the video, but I should have, and it's very easy. This piece is behind the mixer cap and just slides out. No screws or fasteners.