what's happened throughout history is that DOB in their "infinite" wisdom has always sent the oldest/high(est) mileage RTS' to brooklyn after a certain point.. and in more recent history, the DOB usually "rewards" brooklyn division with new(er) buses with the next bus purchase order.
case in point, when i attended Roy H. Mann JHS in the 90's, i remember vividly the old 37xx/38xx series RTS' rolling down utica avenue headed for flatbush depot, all former Gun Hill buses.. later on Flatbush was awarded the 93xx/94xx RTS' and subsequently some 52xx's as well.
similar thing happened prior to the 38xx/39xx NG's coming to the bush... and yet again when artics and the 73xx New Fliers showed up.. nothing but POS RTS' in the yard from everywhere else (ulmer, two-six, etc)
brooklyn has historically been the boro buses come to die, at least in my lifetime