Since it's in your coolant banjo bolts, maybe it's corroded material from somewhere else in your coolant system. I've heard of bits and pieces of shrapnel coming off of heater cores, rads, other pipes, etc. How did the rest of the coolant look when it drained out?
You could always send the turbo to Chadwick to have it rebuilt to a big t28.
You could always send the turbo to Chadwick to have it rebuilt to a big t28.