The RB80 is a very low production unit and I doubt the manual is available online.
At least I never heard of it. As most users are very DIR I doubt any of them just placed it on the web on their own.
None of the North American manufacturers (SMI, ISC, Halcyon,C-L, Jetsam)
has online manuals available afaik. The only (semi-) exceptions are the Hammerhead
and Shearwater manuals, but those are 'just' electronics, not entire units.
Dräger, OMG and APD in Europe all have manuals on the web.
That's liability laws for you.
I foung Golem Gear's
RB80 teardown the best info on that unit available. It doesn't tell you how to assemble and pre/post dive the rig, but you get a look at most of the bits and pieces and what they do.