This is in a curio cabinet that holds panels of glass. The plastic getting brittle. And breaking.

I believe the 32-325 long retainer clip should do the job for you as long as the off set is the correct length to secure the glass in the cabinet. I personally replaced mine in my home with the metal version, the 32-314. There are in fact adjustable. I do want to mention that it is taller than your original clip. You just want to make sure it does not get in the way of anything in your cabinet.

I'm afraid I don't know what the issue is. The screw doesn't appear to be damaged, so it might be an issue with the screwdriver itself. Make sure you're using the appropriate size for the screw in question.