You might be able to find someone to re-cone speakers with butyl surrounds. (Re-coning doesn't necessarily have to mean replacing the cone assembly-it can involve voice-coils and surrounds also).
I'm no chemist but I've noticed some white residue that seems to build up with these butyl rubber surrounds. I've been wiping it off with a damp cloth, and following that with an Armor-all treatment. And crossing my fingers. BUT, I believe that Armor-all has silicone, so keep it away from the woodwork,it can make refinishing very difficult (fisheyes lacquer) also could make touch-ups tricky too.
I'm no chemist but I've noticed some white residue that seems to build up with these butyl rubber surrounds. I've been wiping it off with a damp cloth, and following that with an Armor-all treatment. And crossing my fingers. BUT, I believe that Armor-all has silicone, so keep it away from the woodwork,it can make refinishing very difficult (fisheyes lacquer) also could make touch-ups tricky too.