1969 Smith Corona Electra 110 Electrical Typewrinting Machine Jeweled Escapement

1969 Smith Corona Electra 110 Electrical Typewrinting Machine Jeweled Escapement. Only one button not working (+ =) please see video. The knob for RED/BLACK ink it is not working-it is moving but not compleatly.

I did not test the SET - CLEAR buttons - I do not know what they are for. Everything else seems to work fine-no sticking letters. The case have some rust on the hinges. There are some signs of use and age-I tried to show them all-please see all pictures.