My fan operates properly in the reverse direction (counter clock-wise) but only hums in the forward direction (clock-wise). Is the directional switch malfunctioning or could it be something else? Figured that if it ran in reverse, the motor windings & capacitor are OK.

It is possible that the switch is defective. Try moving the lever back and forth and see if that clears the failure.

I'll also bet that you have moved the switch while the fan was turned on too.

It is most likely a bad reverse switch or loose connection thereof.