I watched Rhapsody's Griftland playthrough, and I found a bug. You can kill drusks multiple times because of life pact, and each time you do(not sure which one) it seems it adds another drusk core to the loot. That doesn't seem intended.
Kill one drusk, and let the other drusk live so that it uses life pack to bring their buddy back. Then finish both off and get two drusk cores.