My "spring washer" http://www.pbresource.com/KT-BFLIP04.html#Not is between the "coil stop" and the coil circled in the pic. ( I think the manual lists it as the "core plug assembly") https://www.marcospecialties.com/pinball-parts/A-613-30
NOTE: the coil stop on the Pinball resource page is different to the one on your kicker , the Marco one is the right part
The parts manual lists it a being placed between the "coil bracket" and the coil https://online.fliphtml5.com/vrtyz/axun/#p=118
When I first considered comparing the coil stop you have on your outhole kicker to another one I was thinking of the free-ball gate but looking at it it was different, screw spacing was different.
The top saucer spots the #5 when lit in the upper playfield the 2 mechanisms are similar and have the same coil stop the manual lists it as the "skill kickout"
your spring washer may be installed between the coil bracket and the coil properly on my top saucer it seems to be there but difficult to see.
spring washer (resized).jpgspring washer top (resized).jpg
Bally kicker parts (resized).jpg