The left flipper occasionally stays up, in play and in test. With its EOS switch blocked it slowly creeps up, while the other flipper behaves normally.

One flipper sometimes locks on: cabinet switch contacts pitted and sticking

Cause: The cabinet flipper button switch contacts were so pitted that they formed a ball-and-socket shape and snapped together, holding the switch closed.

Checks

• Inspect the cabinet flipper switch contacts closely for deep pitting.
• Watch whether the switch opens cleanly when the button is released.

Fix

• File the contacts flat (or replace the switch) and ease the blade tension.

Systems

• Bally 6803

Games

• Special Force

Related tips

• Double EOS switches drive the upper flipper
• Upper right flipper completely dead: failing EOS switch
• Flippers dead and voltage reads nonsense: measure to the flipper board ground

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