Oil Seal Design for 365/400 for ZF Power Steering Pumps

I have a question about the oil shaft seal for the ZF power steering pumps fitted to the 365/400 series cars. The seal is a 17x28x8 size with R5 or DB designation, meaning it's a double lipped double sprung metal cased seal. https://www.ashleypower.co.uk/oil-seals-difference-between-r21-and-r23 for reference. The point of this design is that "the dual spring loaded lips, typically used to separate two fluids but can also be used in high contamination situations to keep out foreign materials and to retain fluid".

The above seal that was used in these pumps is pretty much no longer available. Websites I have found with them are in Europe, and don't have shipping options to Australia. I'm not finding any of my local bearing shops or online sellers with them. The pumps were mostly used in 1970's BMW's and pretty much all the classic BMW parts suppliers show it as no longer made.

The pump parts diagram https://www.bmwautoparts.net/en/catalog/parts/75385/0/1329/2160/2350/0/0 shows the seal (item 5) is directly behind a sealed ball bearing, that carries the load of the rotating shaft. Therefore the seal is keeping the fluid in the pump from leaking past it, to where the bearing is, and out into the engine bay. From what I can see they have fitted a seal for separating two fluids, that in this application only separates one fluid. With that in mind can anyone see an issue using a more common R4 or R6 style seal in the pump instead?

 

The pump hasn’t turned in anger in well over 20 years, and having seen a friends pump leaking after not running in about 7 years, I decided it’s best done while I still have the engine out. So it’s apart and I’m committed now. I tried some searches and found nothing prior to going ahead with job, and just went for it. After I got it apart was when I found the drawings, and most of the seals and Orings being NLA. Aftermarket orings and bearings are no problem to find, but that seal design isn’t common unfortunately


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Also, best I can tell is the Benz’s of the era used Febi Bilstien pumps as opposed to the ZF ones our cars have. Happy to stand corrected though. Maybe check your kit against the diagram I linked to and see what seals you have, would be interesting to see.


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Thanks for your thoughts Sam, I think the chance of contaminants entering from the engine bay to the pump is extremely minimal. Bearing 3 that is immediately in front of the seal is a sealed grooved ball bearing, the pic does look unsealed, but the one I removed is definitely sealed, it's pressed onto shaft 1, and in turn pressed into the pump housing, close tolerance fits of course. The only chance of liquid entry would be if that sealed bearing were to have a proper failure, or as you say become submerged!
I will keep on the hunt for the original seal style, but If I can't get one before I need to refit it, I'll take my chances with a single lip seal. My brain says it shouldn't be an issue, but it never hurts to ask around.