Hey TBatti, did you ever get this resolved? Having the same issue on my upper right flipper. I've had the pin for a couple years and it just started doing it. Same as you, when I turn the machine off it stays in the up position. When it's stuck in the up position, I feel a little resistance when I push on it before it comes down.

So I tried to find the issue and it seems like the edge of the plunger is rubbing when it's fully extended. There's a good amount of movement of the plunger, which I've tried to show. LTG Does the plunger need to be greased in any way? These pics are with the play field lifted on the rails, but when it's back in the cabinet, the weight of the plunger would cause it to rub, at least that's my theory. Any thoughts?

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....Or perhaps it's this

Flipper Plungers / Coil Stops

A flipper works by pulling a metal shaft along a sleeve inside a coil.
As you don't want the shaft, called a plunger, exiting the other side
of the coil, there's another piece of metal, called a coil stop, there
to stop it. After thousands of flipper presses, these two pieces of
metal eventually get flattened and the tips begin to spread out.

This is called mushrooming. It causes friction against the coil sleeve
resulting in a weak flipper. Eventually, the mushroomed end of the
plunger will wear right through the sleeve and start tearing the
inside of the coil apart, resulting in a shorted coil and usually then
a complete meltdown of the coil's interior.

That's the basic mechanics involved in a flipper -- the plunger gets
pulled into the coil, and it drags the flipper shaft around in a
circle, rotating the paddle as a result.

My problem turned out to be the coil stop. I had gold dust all over my cabinet so I replaced it on all three flippers. Amazing difference on the flipper performance.