All S 550 convertibles have an electric power top, there is nothing to leak. It's basically a glorified power window. Could it be something applied at the factory or something you applied that is reacting with the top material? Or reacting with what was already there?
Back in the day everyone used to put armor all on the dash and steering wheel until they discovered it left a greasy residue behind and the more you applied it the worse the greasy residue got. This sounds like a similar issue.
The S 550 verts have been around for 10 years and this is the first time I've heard about this.