Do you mean the armature switch that's tucked underneath the relay bank? (Usually underneath the 'SB' relay, so called the 'SB' armature switch.) The one that opens/closes base on the relay armature movement.

That particular switch certainly is challenging to get to. The way I go about doing games involves doing a complete bottoms up rebuild, so when I get to that switch, I've got the score motor board pulled out of the cabinet, all the parts stripped off the board and sitting on a workbench. Then when I clean that switch, I take it off the bracket, clean it, put it back on, and then I can twist/turn the relay bank as needed to watch the action and gap. So it just kinda gets done as I go along.

But with everything mounted on the board, and the board still in the game, I think I'd still be tempted to pull the board out and place it on a bench, so the switch is easier to access and see. The extra time it takes to pull the board and then later put it back is probably still faster than trying to fiddle with it in the game. Might try just cleaning the contacts "blind" and see if that helps first, but it's hard to see.

One other thing I've done is to use one of those dental mirrors and a strong light. The mirror helps being able to see the switch while it's under the relay, but access for cleaning/adjusting is still a pain.