Speedometer gear ratio adapter lubricant?

[Alloyvert]

I finally got my truck on the road and diagnosing a non-working speedo. As part of the troubleshooting, I removed the rear ratio adapter and when trying to manually rotate, it was very stiff. So I removed what appeared to be a plug on side and noticed a lot of hardened grease in the gear housing.

That freed up the sticking and it rotates very smooth. Does anyone know what type of lube is used? I assume it is some type of grease as oil would leak out around both connections like it did while I was flushing it out?

Adapter p/n 1563872 along with a couple photos.

Thanks for any help!