Bruce,
Cool diagram, thanks. I'll pour a cup of coffee and study it a while! (I love these old school exploded views).
Right now the prism is in the hands of my tech who also told me that he thinks there is a mechanical preload that needs setting. It seems that there is a spring AND foam.
I don' know what it is about these eye level prisms and the original F, but I've been enchanted with them and the Nikon F from the day I went to press events with my dad back in the early 70's and met all the seasoned still-photo guys who swore by this setup (my dad worked for ABC television back then).