I'm going to guess that it's Bentonite grease: thick, black, and very sticky. Probably it's most important property is that it will not mix with water, which is why it's used in (Peerless) transaxles. Other types of grease will mix with the water as the gears turn and slowly leak out of the seals but Bentonite grease will not do that. I recently opened up a 25 year old Peerless transaxle and the Bentonite was still thick, black, sticky, and stuck to all sides of the gears and shafts. There was no evidence of any mixing with water or wear on the gears and this was from a John Deere 180 tractor that was used to mow and snow blow.
Of course, if condensation isn't a problem in your area then Bentonite may not be required.
Of course, if condensation isn't a problem in your area then Bentonite may not be required.
