NPC Spawn Issue: Corrupted Goblin?

[Deecay]

So I've spent countless hours camping the Tainted/Corrupted Goblin spawn in Lake Rathe (killing the upper tower mobs next to Lord Berg spawn), probably close to 30 something hours in multiple sessions, I've seen close to 50 Tainted spawns in this time and not a single Corrupted, does anyone know if the spawn is broken or am I just having the worst spawn chance in the world?