Here you can see the cause of the malfunction: the white separating agent between the plates of the capacitor has dried out. It must be removed. The lower plates are for FM, the upper ones for medium wave. The upper ones will not be needed later.

Slowly and patiently remove all the innards of the variable capacitor. A toothpick is good for this.

On the shaft are rotating rotors, fixed stators and washers. Other very small washers are on the upright posts

You don't need to sort the parts, that will come. But be careful not to lose or damage any of the very small parts.