I have the late 1940s version of this typewriter. I can actually explain why the bolts holding the back cover of yours on were sheared off; on the older but visually identical models -all- of the panels are held on with spring clips like the ribbon cover on yours, but stiffer. Toe strip the typewriter down to a naked chassis you just yank on every panel and it pops off. Someone probably just pried thinking this one was the same as the older ones.

Anyway, this "split in half" feature along with all of the body panels being held on with springs, and the general build quality, is why I think this typewriter is the best engineered one I've ever seen. Not necessarily the most satisfying to type on, though it is good, but the amount of forethought that went into its design is amazing.

The one I own used to belong to my grandparents, and supposedly my grandmother could type 130 words per minute on it.