I just tried DC-Fix (fyi you can get the bezel loose with a fingernail). It didn’t really help.

There’s a lip inside the tube so any replacement reflector/optic needs to be about 15mm

Edit: 14.75mm for the first 8.5mm or so, 17mm for the last 1.5mm, with an indent in the last .2-.3mm on the outer rim where the bezel comes down. Pic.