I'm gonna look up the original recomended oil & see what I can dig up, but I had thought about using Marvel Mystery Oil.
I found a reference on the Auto Boardz site that mentioned something called Neats Foot Oil for leather products,... Odd, but ya never know.

But seeing as these items are still being made & installed in things like forklifts, you might contact the Bendix Tech Support Team at TBS.TechTeam@bendix.com. I doubt they are still using leather for the seals, but ya never know what they have in thier books.

1956 GMC 370 dump " 'Tater "
1970 VW Volksrod "the Black Bomber"
2007 Chevy Avalanche
2020 Jeep Cherokee Trailhawk,
2005 Harley Davidson FLHTCUI

I dig all cars, old and new, whether they were hammered out of American iron, German steel, or Japanese tin cans. Being unable to appreciate them all is missing out on a world of great things.
But thats just MY opinion! :P