Pump Seals in more detail


Now I have an idea how the pump seals work (sealing the rotating shaft) .
If you look at the picture/top you see that bigger ring measured 5.6 x 16 x 4.5mm (bore x OD x height). This part consists of 2 parts. The rubber boot around a white material ring. Can the while material be ceramic as it is smooth and hard (and it is like polished around the area where the cup could sit on it)
I believe this is a gliding surface for the underside of the plastic cup (material Bakelit?) to seal while cup is rotating with the impeller.
The thing is that the rubber boot's 16mm outer diameter is a bit less and does not seal very well any more against the housing (16mm bore). All the rubber is hardened and of course then seal is compromised.
I think I can find the correct o-ring (e.g. 5 x 2.5) for inside the cup (5 mm Shaft to the 9.4mm cup bore) but that boot is something else. Maybe a Teflon seal bandage around the circumference would do that job.

I was wondering before at a main water pump in my good old W109 (when it started leaking temporarily) what the inner seal was... I think I saw something similar in bigger, can't quit remember. Can someone answer this question about a sliding seal in coolant pumps. How does this work?
Best, Martin