Constant fluctuation of sound level is usually down to a loose connection somewhere, most often a cable, but as you’ve eliminated that possibility it’s likely the input or output of the pedal. This sort of thing also happens when you have a dodgey power rail shorting to somewhere it shouldn’t be.
I wouldn’t recommend opening it up yourself, it’s a damn complex pedal that one. I’d say contact EHX and see if they can do a repair for you.
