The dealer sticker inside the case indicates that this typewriter was sold in Seattle by Hood Wilson, located at 106 Denny Way. Notice the fact that the phone number on the sticker is only six digits long. On March 16, 1958, these had been replaced with seven digit numbers. At this time, SEneca was replaced by MAin-4.
The ad above appeared in The Seattle Times on September 29, 1957.
Hood Wilson was large typewriter dealer in Seattle. In the early 1960s, they opened a second location in Lynnwood. From 1955 until 1957, they called themselves the "Typewriter Trading Post." By 1958, it had become the "Typewriter Super Market." They changed their name to Century Typewriter Sales around 1962. (Probably because of Century 21, the World's Fair--Hood Wilson's former building is in the shadow of the Pacific Science Center)
Here is the cover of the March, 1958 Seattle Telephone Directory: