Were the GTP2 diff failures in the ring/pinion or in the diff spider gears? The ring gear is huge and looks indestructible.
Did you open the cases to change lubricants or were the diff cases left sealed and stock?
I noticed the same greenish grease both within the diff and on the ring/pinion.
Mine have been refilled with 100K/40K and ring/pinion lubed with Mobil 1 synth grease but not run yet.