Having a problem with the upper flipper on my Bally Strange Science. Pardon my limited pinball lingo as I may not use the correct terms here.

The Issue:
The upper flipper seems to have some slippage in that it does not retract all the way back into the correct position at times. If you move it by hand you can feel it kind of snap into position.

Here is what I think is the problem. Looking at the assembly it appears that the flipper has a shaft that fits into a "knuckle" of sorts. There is a set screw that I assume locks it into place. I am guessing that there is a worn spot on the set screw and or shaft that is allowing it to slip. I have tightened it down as tight as I can but after some play it loosens up again.

Is this a common issue with flippers? What is my best course of action here? I didn't want to jump in and disassemble it until I researched it a bit first.

Hehe ok will do - I also saw that there is a second set screw as well... cranking them both down. Thanks for the insight!