I just picked up a pr. of KG4 yesterday and have the same issue w/ the KD12 passive radiator rubber surrounds. Cracked and need replaced. But the bass drivers are fine. Hoping I can find new rubber surrounds that are inverted like the originals. AuralTone, please post if and where you found the surrounds. Are the inverted surrounds different that regular surrounds (ie- foam roll concave or convex?) Is it just a matter of flipping them over or are they angled specifically for one way?
This is my second pair and I immediately regretted selling my first pair. It's taken me a few years to find these so I am excited to get these up and restored.