Score reels take a long time to reset, or any motor in an EM (pinball, pitch and bat, gun game) runs slowly.

Score reels reset slowly: sluggish score motor or game motor

Cause: The grease inside the gearbox has hardened with age; sometimes gears inside have stripped.

Checks

• Remove the motor (usually four screws to its frame; desolder the two power leads; leave motor switches on the frame).
• Turn the output by hand and listen for stiffness or slipping teeth.

Fix

• First try soaking the gearbox overnight in alcohol or white vinegar to soften the old grease (this adds no new lubricant).
• If that doesn't cure it, split the gearbox, clean and re-grease it.
• Replace stripped gears, using a donor motor for parts.

Systems

• Electro-mechanical

Related tips

• Vari-target doesn't fully reset and the score motor keeps running
• Motor coasts past its stop: broken armature spring

Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part Two, Clay Harrell (pinrepair.com)