I use a pair of Swift eyecups as applied on post-1985 Audubon 804 (HR/5) and other models of Hiyoshi's design. They simply slide over the Leitz' cups, fit snugly and can be adjusted in height. If you're satisfied a few drops of glue will keep them in place 'till the end of time. see pics.
Renze
Hi Renze,
Many thanks for your suggestion, I will still search for a replacement cup, as one is broken badly, but I will also try that, as they look in your photo as though they are far more comfortable to use. In fact that has given me a few ideas, for other vintage binoculars I have, in particular a hartmann 7x35 polerim which I use quite a lot, it is a comfortable wide angle binocular, but your idea may improve it further. Hartmann are somewhat underrated, in my opinion, they made great optics comparable to zeiss at the time.