a video of the ratchet side would be good if setting the spring tension and making sure the pawls / arms are moving freely doesn't fix it.

especially check the pawl next to the reset coil ... half of its job is to make sure the ratchet moves one tooth per activation of the reset solenoid coil.

it looks like the pin the reset pawl is pivoting on is loose and wiggling around ... is it?

if the pin is bent or flopping around, the pawl may not engage the teeth reliably.

is the pin bolted to the base plate or is it the pressed in kind? If pressed in, time to scrounge a replacement plate.

when the countdown stops, does the ball eject (bonus score relay loses power), or is the bonus score relay still powered but the score motor isn't running?

if the bonus score relay is powered and the score motor is running, check the switch on the bonus score relay with wire 31-1 on it and the plug connection to the playfield for wire 31-1.

if the peg on the ratchet/gear can't push the zero switch(s) easily, try adding a 1/4 turn to the torsion spring until it does. Then verify the unit will step up all the way without struggling at the top step.

you pretty much want the long blade the peg is hitting to be barely touching the peg when the unit is stepped up once. That'll give maximum blade travel when the unit is reset. Then adjust the short blade for correct switch action at step 1 and reset.

the unit base plate was used on a lot games ... including EM slot machines of that era. If you have trouble finding one, pm me and I'll see if I have one laying around. If I don't, the pacific pinball museum should have plenty of them and I can dig around in their warehouse.

the plate is easy, finding one with the correct reset pawl is harder as step-down units were less common. If the pieces on your plate are good, then you can swap those on.