I rebuilt three of my kickspace heaters a few weeks ago. They’re not Cadets, but I think they’re all built about the same. Mine have an auto-reset limit switch (looks like yours) wired in series with a thermal fuse. I think the thermal fuse is intended as the backup, since it is a one-use component. I bought new limit switches, but decided to reuse the old ones. My dead fans are what triggered the rebuilds.
After cleaning out 35 years of dust, I was able to reuse everything except the fan motors and blades. The metal blades were fine, but the new motors are slightly thicker, so I had to find blades with a flatter pitch to maintain clearance in the enclosure. I found it interesting that each heater was configured to use only two of the four heating elements (you can choose to use all four), so I effectively have two built-in spares in the unlikely event an element goes bad. All in, I have about $30 and an hour of my time in each one, not counting time spent finding the fans and motors.
The first photo shows a fan before the rebuild, with the thermal fuse under the white fabric to the right of the limit switch, which is under the cardboard. The second photo shows a different heater with two unused heating elements.