Find a screwdriver that is thin enough to go under the ring, wide enough not to crease the metal and soft enough not to mark the plastic and then a lot of patience.
Think long and hard about going in there if a new cable is on the way. A small bit of lube at the cable entry and then see how it behaves.
Don't ask how I know this
Yep, you can remove the glass quite easily without leaving any traces visible from the outside. Basically, use a very thin, small screwdriver blade to pry up the back edge of the retaining ring a wee teensy beensy tiny bit at a time. It takes a little patience and usually at least two or three trips around, but eventually you'll be able to remove the ring and the glass to get at the mechanism. (There are also a couple of screws to remove, but they're obvious.)
To reinstall, you'll use something small and smooth to re-crimp the edge. Take tiny bites and make several trips around, and the evidence will be barely visible. And it will be hidden by the "gasket" ring and outer housing.
You do NOT need to cut the housing open.
