Based on the replay jacks in the head of the game, what are the replay values? I'm wondering if only the 1k to 9k jacks are set at the 1k position. I'd expect this to impact all player, but it is at least something to check..

Still does it if you unplug all the score adj. wire plugs? Are you getting a replay knock too, or just credits?

I thought this might be a clue, but looking at the schematic, this is correct behavior - only the special-based add replay is cut off when the replay unit is at 15.

That is odd, both the points replays and the matches DO NOT go through the 15th Pos Replay Unit switch. So you continue to get the knocks above 15 credits for everything but specials.

EDIT: Looking thru some other schematics, this is common... NVM

My schematic shows paths through the match unit, 2nd coin chute, and through the thousands reels via the high score point adjustment.

When “L” fires, it travels through P1B,
to the first player thousands score reel,
through the high score adjustment plug,
to the ten thousands score reel,
then P1A on its way to the replay unit.

So when you have the plug set at 55,000, when the 10k drum is in the “5” position and the 1K drum is in the “4” position (54,000), a path is completed to “L” so that the next time “L” fires (you score 1,000 points, moving from 54 to 55) the Add Replay Unit will fire.