Ok I heard back form Luigi. He indicated that producing a strap with a rubber grip facing on his leather straps would cause him problems in exporting to the USA. Seems that he has to declare the materials used and "all leather " except hardware is what he is cleared for.
He doesn t think the strap needs it and said he has heard no complaints.
Billingham ,maker of fine camera bags, has just come out with a " new version" of their removable shoulder pads . They are leather,lightly padded and have a flexible rubber facing. Might try one of those on his old strap without the pad .