Los Angeles, CA
If the flipper sticks up only when the game is on, then it's a coil issue - you'd best be advised to replace the coil and diodes, since it's likely that the coil is a bit burnt at this point.
If it sticks up whether or not the game is on, then there's a problem with the flipper plunger or sleeve. The sleeve may be cracked or the plunger may be mushroomed out and getting stuck. If that's the case, you need only replace the plunger and sleeve, or if you're feeling enterprising and can't wait for a replacement, you can use a dremel to shave down the mushrooming on the plunger.
