Late MGB heater controls, control cable replacement

We have a 1978 MGB in the shop in which the heater doesn’t work. We start by verifying if the heater control valve is actually working and find out the cable simply isn’t moving while turning the knob. Turns out that issue was only a loose screw but after tightening it, we realized that it was also stuck on defrost only so the air could not be diverted to the floor or turned completely off. Upon closer inspection, we discovered the air control knob wasn’t moving the flap in the heater box due to a completely different issue with the cable than the heat control had, necessitating a cable replacement.