next time it sticks try taking the glass off and see if it will drop down if you press down lightly on the end of the flipper.
I just want to check if the coil is staying energized or not.(if you feel strong resistance when you push down on it and it wont go down then we will know that the coil is still on)
i know you said its not binding but just worth a try.
i have 2 pins which have a sticky flipper both of them are the left flipper.