I can post some video later today on my game.

Well here is an older video (not mine) showing normal operation.

Yeah, each advance through the pit is really 2 stages. I was thinking it was a mechanical issue - good job on finding the missing part. Gotta love the (free, detailed) Bally parts catalogs.

I took some video anyway just to show the mech in action, close-up:
https://www.dropbox.com/s/2aq5hrirpo5xgk2/4MBC%20tar%20pit%20mech.MOV?dl=0

Sounds like they wanted to make the game easier.

With apologies to the OP for going off track...

Not my game video, but I have mine set the same way. Bell choices are: never, w/ 100 pt re, w/1000 pt re, w/ 100 & 1000 relays.

For me the best part of the game is the skill shot and the extremely high 3k you get for it when you roll back down the ramp. With 1000 pt only bell setting, the game is admittedly a bit quiet, but you get 3 quick bells for that skill shot which I think highlights the shot. At no other time (w/that setting) can you get that. So I can be in the other room and know that someone hit the skill shot - I like that. If I added bell for 100 too, a ball in the lit pops gives you tons of bells which sounds nice, but kinda dillutes its significance. I also like that I can keep track of my score in my head if I limit the bell to the 1000 pt reel.

But that's just me.

Is your ball making it to the ramp area ok? Mine wasn't and I didn't see any directional/guide adjustments. But cleaning, waxing and tweaking of the playfield pitch did the trick for me.

If you are talking more about troubles with power than direction, I would think that clean parts would make things consistent. You can also do a slomo video with a cell phone to see how the ball might be stuck off-center or is rattling around before it exits shooter area.

Good job, Hopefully you will find a solution soon. When you do get it working, keep in mind that you will get 2 balls in shooter lane if the game thinks there is a ball in the tar pit, but it isn't.