Congratulations, VacmanSpencer1982; looks like it's it's been well-maintained. Hopefully you'll find an original-style bag for it. Btw, even though the base is stamped 1981, that is technically only when the base was made—at least that's how Eureka operated. That's not to say the complete vacuum cleaner was assembled later, but it is a possibility as I have seen on Eurekas before. Just something for you to keep in mind if you happen to get more Sanitaires and may find supposed inconsistencies in feature updates or whatever.
Here's a 1979 ad for it and other commercial uprights: