Despite my earlier trepidation I decided to crack open the right Bin Bok joycon to see if I could figure out what the problem is. Forgive the overzealous flash:
I didn't immediately notice anything wrong, but I took a q-tip w/ rubbing alcohol and tried to clean in and around the ZR button as best I could, both within the casing and around the back. Unfortunately this button doesn't seem like it can be removed from the rest of the backpiece, at least not without applying enough force to break the endpieces on either side holding it in place:
It's also held in place by an overhanging "lip" on the trigger itself that stops it from being pushed through at the angle it's set in (didn't get a picture of that but joycon owners know what I'm talking about). A considerable amount of force is necessary to push those pins out of alignment and below at which case the trigger can be angled to slip through (maybe), but I don't think the plastic could take that kind of punishment. Anyways I cleaned it up best I could and set both halves back together but the trigger still sticks when pressed. I'm running out of ideas.
The problem seems to be purely mechanical: the actual button on the circuit board can be pressed and depressed with no issue, it's just the plastic trigger doing the pressing that seems to cling to something when let go. I have to pull at it to get it to free itself. I'm going to run the backpiece half under some warm water and see if that does anything to free things up.
EDIT: water didn't seem to help, so once the plastic dried out I tried taking the smallest flathead screwdriver I had and rubbing vigorously in-between the plastic seams where the trigger sits, hoping to scrape off some of the plastic around the button where it seems to stick the most. After doing that for a bit and shaving off a miniscule of plastic I put it back together and it seems to have done the trick, the trigger doesn't stick anymore. I'll need to play with it for a bit and hope it stays that way.
