Hey there - had the exact same issue (In my case one of the caps was actually leaking). Huge thanks for the tip - I also noticed that the glue which holds the permanent magnets in the drivers, brittles over time making your speakers sound “metallic“ and a bit quieter as the magnets dislodge - mine came out when I was moving. Easy fix is to press them back in and re-apply some glue to hold them together for another few years .. (do take care to match them to the right drivers they came out of or they will sound weird).