These machines came with gear oil. There is an oil level check plug, thus implying that a specified level of fluid was required inside the cases. Snidal (hallowed be his name...) in his manual just adds motor oil until it appears at the level plug, then buttons it up and lets it churn for a couple hundred miles of riding, then drains out the resulting mess and replaces it with gear oil. A couple cycles of this and you are back to where you need to be - gear oil lubricated bushes & gears. All three of my Bullets had "greeze" inside the cases; all three got gear oil (140W85) and the only "leaker" had a split clutch pushrod bearing cap that had been "fixed" with silicon sealant. Amazingly a new aluminium cap cured this.
Grease is an affectation, a nod to the excessive fastidiousness of "collectors" (and older US & Euro Honda/Yamaha/Kawasaki/Suzuki riders reliving their youth...) that aren't keenly interested in finding a dime to 50 cent size splotch of oil daily below their showpieces. These machines aren't Hondas, there will be weepage of internal fluids. They were intended for daily-driver transportation and maybe weekend joy rides with the squeeze du jour. In 1935 a bit of oil leakage wasn't a big deal. Keeps down the dust, right? So do the Snidal oil purge and don't look back. I use 140W85 simply because on hot days on my bikes the shifting is still "agriculturally OK" and not getting "notchy" at the end of a ride, YMMV. These machines aren't the Space Shuttle, but they are pleasantly close to their infernal combustion roots. Toss an old towel or t-shirt under it and enjoy your time machine.