I'm not very knowledgeable on EM machines but it sounds like you are missing a part, are you sure nothing came of the leaf switch? Is the leaf itself broken? Did you find any loose parts in the cabinet?

sometimes the leaf has a bend in it that goes above where the ball will rest after a drain,
kind of like the letter 'P' but 90* to the left.
Yours may have broken off check to see if an extra piece of metal exist in the switch stack
and look for any broken parts under the large relay board
you can bend your own with a scrap piece of metal and place it in the leaf switch stack.
I'll look at the 1970 Bally I havent fixed yet and try to get you a photo,
good luck with it.

I checked the 1970 Bally pin in the garage and found that a small peg or barrel fits on the end of that switch leaf and thats what the ball rests on, it's 3/16 wide and 7/16 long with a smaller pin on the end (3/32 dia.) that goes through the the sw. and looks like a rivet type conection. (sorry I cant find my metric conv. chart) I bet it just fell off and may still be in the machine. I have two photos from my machine that I took tonight if you want them.