Thanks for the response and especially for the links. Yes there is only one small patch where the coating is missing but the rest of the coating on both horns seems very well bonded. But can't really know for sure so I will heed your warnings. Would the aquaplast normally be soft and pliable or hard?

Think I will try the Acoust X - the OEM aquaplast would normally be what I would use, but I may need more that 4 oz perhaps. I'll just need to do some tests to ensure the Acoust X is compatible. Surface prep for both the coating and paint is a bit of an unknown - guess I'll just need to experiment gently...