roadholder forks , on mercury 650SS

My 1964 parts list (too early for yours.. ) only lists leather washer for G15CS, which had rubber gaiters.  Price 4d.
But it lists a 'washer' price 3s 2d for all models.  Probably steel.
No idea if this helps.  But might the leather have been an attempt to keep water out, especially if the rubber should split?  Does yours have rubber gaiters instead of metal covers?