Your particular style of coil bobbin does not use a brass spacer washer at the back of the bobbin. The back end of your bobbin has a thick plastic covering around the coil core that provides the correct spacing of the coil bobbin in the relay frame. This photo illustrates the difference. The bobbin on the left uses a brass spacing washer. The bobbin the right (the same kind as yours) does not use a brass spacing washer.

coil backing (resized).jpg

As for the sticking Z relay, have you cleaned and dressed the face of the relay armature? It sounds like your Z relay could be sticking mechanically, rather than being magnetized. Here is a related post that describes the issue I'm talking about:

https://pinside.com/pinball/forum/topic/jumping-jack-scoring-relay-sticks-sometimes#post-6014112

- TimMe

That pic in your post #9 shows the brass mounting screw, not the brass washer that MarkG was talking about. The thin brass spacing washer (if your relay had one) would be located between the back of the coil bobbin and the inside of the relay frame. However, as I noted in my post #11, your relay does not use a brass spacing washer, so you won't find one even if you take the relay apart (which you should do, in order to clean the inside face of the armature and the face of the coil core).

- TimMe

Yeah, the bobbin form-factor is not related to the coil part number. Gottlieb updated the bobbin format a few times over the decades, usually without changing the coil number. The earliest bobbins were cardboard and fiberboard, which were updated to plastic in 1960s. The final version of the bobbin with the thick backing came into use in the early 1970s. The Gottlieb part number of that final bobbin version is D-15341, which you can see molded into the front face of the bobbin.

- TimMe