A stab in the dark. I wonder is the meter works on the same principal as the one fitted to the NIkon F1 and F2 Photomics where there was a carbon track which acted like a rheostat, so altering the current to the meter, depending on the light entering the lens. ...
It's simpler for the Leica, as the light striking the photocell is always coming from the lens at the selected aperture. All the metering system then needs to know is the film speed and shutter speed.
With the Nikon (or other SLRs), the scene is metered at full aperture regardless of the aperture you've got selected. Therefore, when you turn the aperture ring to select an aperture, there needs to be a mechanism to tell the metering system two things: First, the maximum aperture of the lens (telling the meter that, for example, the light it's seeing now - wide open - is from an f/2.8 lens). Second, it needs to know the selected aperture so that it can calculate how much less light the actual exposure will be made at.
The first criterion was satisfied by, after mounting the lens, you performed the Nikon Aperture Ritual of twisting the aperture ring to max and min settings.
The ring resistor was part of the second criterion in that as you turned the ring, the "rabbit ears" indirectly moved the contact on the ring resistor in the head.
