The R4 compressor and its clone aftermarket imposters have used a number of different combinations of seals over the years. You will need the right seal for what you have. The metal/rubber combos come in atleast three thicknesses and are the only type seal used on real Delco/Harrison R4s for the last ten years.
One other problem we are seeing more as the cars age is the bowing of the manifold assy from overtorqing the single attaching bolt. This makes resealing impossible.
Bosch Master, ASE Master, L1
33 years MB technician