Adjusting the ribbon vibrator on a Corona 3

The folding Corona 3 typewriter has a ribbon color selector. That's the little switch just right of the left spool cup. On this particular machine, the 'black' setting did not lift the ribbon enough for a full character print. Didn't dare to mess with this compact mechanism back when I got it, so just set it to the 'red' setting and used that.

When asked to fix a stuck carriage (by my eldest, who's sort of taken ownership of this one), also had another look at this vibrator linkage. The gully that guides the roller that lifts the arm that pushes up the vibrator seemed fine. The roller is a bit worn, but not too bad. The gully itself is fairly rigid and in the shape it should be.

Then spotted that the switch end-positions are not given by the slot. Two 'flying' tabs at either side of the switch baseplate act as the stops. (The shape of the switch-part should have been a hint...) The spring-loaded switch is always pressed firmly against either stop. The shape of these 'flying tabs' is similar to other Corona adjustment features I've seen on Speedline machines, the shape suggests they are meant to be tweaked.

By carefully forming (that's bending, but you meant to do it) the tabs with pliers, the height of the ribbon vibrator for both positions can be adjusted. The left tab controls the 'black' position and the right tab the 'red'. Gently moving the left tab towards the switch increases the lifting height of the vibrator. After this adjustment, it again prints full characters in both settings.

Wondering; how ever did this come out of adjustment? Or did this particular typewriter never really work well on the 'black' setting?

More little mysteries to ponder :)   such as why the carriage seemed wedged stuck, but now loosely follows its guiderails again...