Hi Coburn
I have a bit of a theory on that.
Just as the HW35 changed to a nylon seal with the introduction of the HW80, could it be that the 25mm cylinder Weihrauch guns changed from leather to Nylon seals with the introduction of the HW77 in january 1984 ?
Though it would seem strange if Weihrauch did carry on producing leather seals at 25mm four years after the introduction of the 30mm Nylon seal.
All the best Mick