dragon scoring issue...

We are nearing the end of dragon but there are two major issues I have to attend to.
First, the player motor is super sluggish so I will have to dismantle it and clean out the old gunk.  Apparently it is a bit finicky, so I will have some external help for that.

The second issue is a but more mercurial.  I have yet to find the scenario where it reliably happens.
Somehow, the thousands and ten thousands solenoids get linked.
Thousands advance, and at the same time the 10k solenoid advances as well.  If I manually close the 10k solenoid in the back box, the 1k one also fires.
This happens for ALL PLAYERS, so it isn't a sticky carry switch in the score reels.
It also happens when I am tapping the side buttons for 100 points, and when I roll over 900 to 1000, the thousands firing also fires that ten thousand.  That means the O relay, which uses pulses to score 5k, is not the culprit.
It is also not related to any specific scoring switches on the playfield.
So, somewhere in the backbox, right?  We have the player motor stack and the relays for hundreds, thousands, ten thousands, and hundred thousands.  It FEELS like something is wrong there but I am foiled at each inspection.
I'll post the relevant schematics later, as I on mobile, but there are only so many triggers for the 10k reel:  zeroing advance logic, rollover from 9000 points (carry bit from each player,)  bonus counting, and 10k pops. (More? Will check later)

The most frustrating part if the investigation is that it isn't always happening, and I can't quite discern what is different when this issue is occurring.
When the 100k rollover happens at the same time the system is often stuck a bit since (I assume) it doesn't have the juice to advance all three score reels at the same time.  Since the advancement doesn't complete, the relays are still in the on position, and the scoring sound stays on like a squeal until it properly advances.

I am a bit stumped about where to investigate, because there are so few places where the two scoring mechs could short, and the intermittency just makes it worse.