I don't know of any downward octave glissandos.
Brahms's Paganini Variations (Book I, Var. XIII).
These would be extremely hard to play with the RH so I doubt that Beethoven meant these runs as a glissando.
Indeed Beethoven meant them as glissandi in the Waldstein Sonata (as well as in the First Concerto), at least, according to musicologists and historically informed pianists. A clue to that is Beethoven's original fingering, which indicates 1-5 on each octave, quite redundant if that weren't the case. As to the difficulty of octave glissandi on a modern piano, yes, they are troublesome, for sure more troublesome than on Beethoven's times fortepianos, whose key dip was shallower and action very light. Arrau himself could drop the Waldstein from his recital program, if the instrument wasn't properly regulated.