So, in Wowhead said drop rate is 4% but is around 0.5%. I farm them and after 100 mobs i got only 0 drops haha. After that i continue and after 238 mobs i got 2 Essences. Do you realized this is whole day farm right on 55 to 57 lvl NPCs? At least put some silver to drop for repair after these longs fights for repair 