Orignaly 90W . If it is a leaker a lot of people put in chassis grease. Another thread lately said STP or Lucas which would be better than grease.
I would not reccomend wheel bearing grease. It does not flow. For what it is worth some of the guys on the Falcon website really like John Deere cornhead grease. It is plenty thick and comes in a grease gun tube so it is esay to get into the box.
Gear oil may run out with the seals no longer being perfect. I'd drill a hole somewhere safe, screw in a Zerk fitting, and pump in some chassis grease until it started oozing out somewhere. I've even done this to my 38 Chevy vent window gear boxes
I'm surprised the guys from the northeast even know what John Deere cornhead grease is, but yes, they are right on. Kind of a cross between chassis grease & 90 weight gear oil.
Shell makes some Semi-solid Grease that is ideal for this. It looks like chassis grease but actually flows (slowly) but does not run like 600W.
We used to make our own at the shop I worked at many years ago. Good old wheel bearing grease and 90 wt gear oil mixed in a coffee can until the desired consistency is reached. Thick but fluid enough to flow back between the gears.