Unless there is a short or arcing occurring in a panel, I'm not sure how a panel can cause this. I am attaching ML's panel replacement instructions. Essentially, the audio signal is fed through a step up transformer and connected to each stator (one on each side) and they are separated by spacers that also support the mylar transducer. A bad/shorted transformer or stators could blow out the caps causing them to overheat and boil out the electrolyte contained inside. Without a schematic of the board I can't tell what other components could fail to cause the issue but because we see it on both speakers and it is highly unlikely they both suffer from the same defect, I would suspect something in the input over driving the boards such as heavy clipping or a very sharp transient spike. The speakers are rated to 400W but a transient can easily cause a 400W amplifier to produce spike many times greater. Of course, if they somehow got wet with salt water that is our hell on electronics, even those designed for the marine environment.