rogue mono switch on 82

The monitor bank mono switch on my 82 is always 'half on', even when it isn't engaged. To begin with (around february) it was very faint, but it seems to be getting brighter as time passes, albeit slowly. I haven't noticed any deterioration in sound quality, but might it bode bad things for the future? Has anyone had the switching bit go belly up?

Or shall I just leave it to its fun?

Oh the joys of buying second hand.

Thanks for any info.

Jon