Last week while riding home, I noticed my 8 speed ultegra bar end shifter wasn't "clicking" as it should. I noticed that the flat head screw which held it together was loose, so I tightened as best I could with the flat head on my multi-tool and got home.
Once home I disabled, greased the screw and tightened things up properly. Yesterday I noticed that some of the index points aren't working. The lever physically moves the rear derailleur, but over certain cogs it's strictly friction.
Things basically function, I can use the entire range of my cassette, and am not above using friction mode since this is my commuting bike.
What could be causing this?