Finally got the fossorial bile larva, it only took three years of randomly skinning things while questing. It has totally not driven me insane 
I was travelling to the Tar Pitter world quest and skinned all the marsuuls everyone else had killed and thar she was. Also, by coincidence, got the Army of Light toy from the gleaming footlocker on the same day, which I had also been farming for three years.
Does this mean, perhaps, that I’ll finally get the thistleleaf adventurer at the next Dreamweaver quest? Oh, pleaseohpleaseohplease.