So you think it's completely done?
The voice coil, yes. I'm not trying to be the bearer of doom, but I'd bet $1 (or more!) that the VC is baking and on its way out every time you send power to it, especially if you're sending it any high frequencies at all (even as simple as a tone knob turned open on your bass). And at this point, not even flats on a Pbass with all the highs killed are going to make it go away.