You Can Rebuild....
....A TriStar motor, but it isn't jolly likely you'll need to.
Due to the three-stage filtration inside the machine (cloth bag, paper liner bag and motor filter), TriStars stay pretty clean inside if taken care of, reducing wear on the motor a great deal. And there is one more stage of filtration after the airflow goes through the fan - an afterfilter on the exhaust. You don't see dust resettling soon after vacuuming thoroughly, the way you do with some other makes.
My mom The Appliance Killer had a Compact C-2 she didn't take care of - she used only the cloth bag, disdaining the "expensive" paper liner bags, and she never, in all the time she owned it, replaced the motor filter. She only knocked dust from it from time to time. Well, actually, she told one of us kids to do it. Anyway, that machine STILL lasted over thirty years, until she killed it by vacuuming up wet stuff, then putting the machine away without emptying it, then leaving it in a storage closet for some weeks. She was very annoyed that it wouldn't work after that!
Yes, there were TriStars in the U.K. - there was a 240-volt version for that market. They aren't common, but they're well worth seeking out if you're a Briton.