[Saxhound]

Don't trim the felt. It should be attached to a threaded plug that you can (carefully) adjust with a large flat bladed screwdriver.

 

[Saxhound]

I didn't realize it either. My C felt kept falling out, and I would studiously remove all three screws and the entire key guard, and try to glue it back in by inserting the felt with a pair of tweezers. I finally took it to my tech, and was embarrassed to see how fast he zipped that thing out of there. Other lesson learned - once a piece of felt has dried glue on it, it's almost impossible to re-glue it and have it stay on for any length of time.