A button fitting issue resolved - sort of.

[shortrackskater]

So, last night I did a clear/key on my s2000. It was putting the coin to credit only, which was annoying as hell. After two attempts (since I pressed MAX BET one time too many  ) I got that fixed.
Then I noticed my SPIN REELS button light was intermittently off and on. It wasn't the bulb - the housing had cracked and the bulb socket wasn't holding in. Ok, this should be an easy fix since I have spares. I break off the old one since the nut was stuck, and screw on the replacement. I pressed the socket/bulb in at the bottom... so far, so good. Then I try to press the lens back on the top and it just lays there, and won't snap on. I try rotating it 90 degrees and nothing. Both housings were EXACTLY the same size. So I remove the white part that houses the spring and compare them to see the part that the lens slips under and locks is lower than the other! Why would IGT do this? Or, was my replacement older, or perhaps for a Bally?
To fix it (so I think) I just replace the spring housing with the old one and the lens locks right in.
Great! But, right when I popped it in, another problem came up...well that Was the problem: it didn't come up - the lens that is! It was too tight in the black housing now! 
My final solution was to carefully file the inner perimeter of the black part. I also ran my handy feeler gauge around it to open up more space. Now it works.

[cowboygames]

I've ran into that before and used an emery board on the white part edges to loosen it up

[shortrackskater]

I'm still curious why there's two different types of spring retainers. 
This was the black part, for my case. The white spring retainer fit fine. Weird.

[cowboygames]

Yeah, the part in your first picture. I filed the 4 sides of that so it rode inside the body (black part) of the switch better. I think it was probably S+ versus S2000 and they switched suppliers. When the inserts where imprinted with whatever legend (S+) the base of the switch seemed to be slightly smaller than the switches with insertable legends (S2000)

[shortrackskater]

That makes sense... although if I had used the new button entirely and filed the edges, the clear lens still wouldn't pop on due to the ridge being in the middle and not toward the bottom. I still wonder why they put that in a different place?! But like you said, maybe different manufacturer/design. I'll have to pop off one one of my others from an S plus and see what it looks like.
I've got a few more weeks recovering from surgery - so while I'm messing with buttons, maybe I'll play with my colored LED lights and see if I can burn up some things too!