5711, air in powersteering system

My 1978 5711 have a lot of air in the power steering. When looking in the power steering tank with the engine running idle, the oil that returns to the tank is mixed with a lot of air, no steady flow at all. Also, when moving the steering wheel, it takes a couple of seconds to build up pressure.

I don't see any leaks, only a few connections sweating a bit. It seems to me that the only place that the system can draw in so much air is the driveshaft in the power steering pump, and if so, I probably also end up with ATF in the engine oil...

Which kind of gasket/seal is in the power steering pump? Simmerring of some standard/metric kind? Is the pump repairable or is it a only replacement that is an option?

Anyone experiencing similar problems?

Since I made the conclusion that the pump was leaking thru the driveshaft seal myself, I removed the pump and my hunch was obviously correct. Lots of red ATF on the engine side flange:


And the reason for the leak was also very obvious: The shaft seal (zimmerring 35x25x7) had been damaged when installed: The visible damage fits exactly to the splines on the driveshaft:


Anyone have a split view of the pump? There are a couple of washers on the driveshaft that I'm not quite sure which way and in which order...

A new zimmerring and an hour work and my power steering works like a charm No air in the return pipe.