After a morning drive in my 1924 cut-off touring (now a pickup), I decided to pull the floorbards and the transmission inspection cover to clean the screen. Looky what I found stuck to the screen magnet, a Bendix key! Since my starter works fine, this must be an extra one that popped out and fell into the starter hole some time in the past during a Bendix change/replacement. Took all this time to get flung up high enough to get caught by the screen magnet (my car came to me without a magneto and with oil slingers on the flywheel).
Oh well, now I have a spare!
Always nice to have a spare! Glad you didn't have to find it the hard way.