The way these flippers work is that when the button is pushed, it activates a the solenoid (seen here with a torn cover) that pulls a piston through its center, cranking the flipper on the top of the playfield. What's clever about flipper solenoids is that they're two solenoids in one - a high power coil and a low power coil in a single unit. When it's first activated, the high power coil gives the flipper the energy to propel the ball all the way up the playfield. Then, in the fully-depressed position, a tab on the crank opens an "end of stroke" (EOS) switch, changing it over to low power, so the player can hold the flipper up without burning out the coil.
As you can see in the photo above, the EOS switch is bent all out of shape, so only the low-power part of the solenoid was activating. Trying to re-bend it back was a futile effort.
I replaced the coils and the EOS switches and once again, it's flipping as it should! Let those spinners rip!