After the game has sat unused, one flipper works intermittently even though the coil measures correctly.

Flipper works only some of the time: clean the button leaf switch

Cause: Dirty contacts on the cabinet flipper button leaf switch.

Checks

• Watch the flipper button in switch test while pressing it slowly; it should register cleanly every time.
• Measure across the button switch contacts with a meter while pressing it.

Fix

• Clean the contacts (for example by closing the switch on a folded piece of clean paper and pulling it through) and adjust the blades so they meet firmly.

Systems

• Sega/Stern Whitestar

Games

• Lord of the Rings

Related tips

• New flipper assembly won't fire and blows its fuse: coil wired by habit, diode blown
• Upper right flipper only fires on a full button press: that's by design

Source: Pinball Repair help group!! (Facebook group)