I recently bought a second-hand monome 256 (that I think is a number of years old, good condition but walnut casing, cumbersome, etc) and it seems to work absolutely fine except the ‘level’ osc messages have no result whatsoever.
What “other ways” are you changing the brightness? Are you referring to the intensity messages that set the whole grid’s brightness? Can you change the brightness of individual keys with "…/level/set"messages?
Perhaps I’ve misunderstood your post or you’ve already seen this, but some of the older grids only have a single level of brightness available. You can verify your grid edition here: