what's wrong with it? maybe "we" can help...

You can also contact the appropriately named user:
https://pinside.com/pinball/community/pinsiders/pinballhelp
(he's in NO, and has many videos up on Utube, including one of a Lawman, that he has repaired)

cool,
I just picked up a Lawman a few weeks ago myself, but haven't had a chance to work on it yet. I believe the horseshoe advance feature works with a mini-stepper (AS type). This has to be adjusted correctly, or it won't execute the proper bonus advance. I would take a close look at that first. Hopefully, you have the schematic and can reason out the circuit that adds bonus from that stepper to check out as well. Let us know if you have any success.

If the horseshoe lights advance, but the bonus doesn't increment upward, the AS unit is working, but it could be that one of the small switches mounted on it isn't making contact when it completes a revolution. On that particular AS, there are two cam controlled switches; one is the zero position runout, and the other is the bonus advance. They are totally opposite in their operation; the runout switch is closed until the AS reaches the first position, and the bonus count switch is open until the last position is reached, then it momentarily closes to add one bonus level. Check to see that the horseshoe resets to the start position at the beginning of the game, and at the start of every ball. That's what it should do. If so, this would also indicate the AS is working, but that the add bonus switch is likely not making.