Here is a link to a history of the WMS company, currently a maker of slot machiens. It appears WMS (formerly Williams Manufacturing Co.) was purchased by Seeburg in the sixties. My guess is that ended the manufacture of slots with the Seeburg name. Future machines were called Williams, or as they are now, WMS. Seeburg was renamed Xcor Intl., and seems to have disappeared as a company in the 80's.

Since your machine takes 1979 dollars, it may have originally been another denomination (25c?) and later converted to a dollar. Or it could have been actually made by Seeburg under their own name before it purchased Williams. More research is needed, maybe for a service manual with the makers name and date?

http://www.company-histories.com/WMS-Industries-Inc-Company-History.html