IGT S Slot Machine History

[Anewagin]

I read the link, am I to assume that the S-plus machine then was made in 1990?
I can't believe it's so hard to find that information.  I have searched Google every which way to find out what was manufactured when.  I didn't even know that they made an "M" machine. 
What year is yours? 
Tilt says he has one that was made in 1986, the same year the S-slots were introduced.
So far I like the machine.  It has a few quirks, but nothing I can't live with.  I will start keeping my eye out for parts.  For starter, buttons.  The buttons don't all match, and I'm not even sure if they are correct to the S-slot machine.  I am still doing my research.
 

[therockinelvis]

Yes the buttons plug differently. If I remember right they twist or maybe it was the bulb. I know I broke one and replaced it with one I think from a PE??? Think Sizzler gave it to me.