Vanchester,
Welcome to SCF!

The stamp you have can be a Scott 229, 251, 280 or 271 depending on its watermark. Colors are not exact on a scanner (or this series) so it could also be ultramarine, Scott catalog numbers 336,437,463A,473 or 482 again depending on its watermark. It is part of a long and complicated definitive series called "Série Vovó" that was issued from 1928 to 1941.
The Brazilian catalog, RHM, doesn't list plate flaws so it isn't much help. There are lots of minor color variations etc. so I'm not surprised that an occasional plate flaw like yours will show up.
I'm sorry I can't give you a feel for its scarcity. Maybe there is a more detailed Brazilian collector that can help.
It definitely is a keeper though!
Edit: forgot some possibilities
Dan
