Actually, the prop shafts are both of the drive shafts, identified as either the front prop shaft or the rear prop shaft. Typically, just called a drive-shaft or a drive-line.
We use BG Wheel Bearing Grease at work, but I prefer black moly grease over anything. It's super sticky and handles heat and stress exceptionally well. I also like using it in the wheel bearings. If it's good enough for trailers towing boats and getting dunked in lakes, well then...
If you have the adapter, or it just has a regular zerk, then you just pump it up until you see the old grease pop out the vent hole.
Some guys pump until you see new grease, but it's not necessary. If you see water come out, keep pumping until all the water is out, and grease follows. If you just put a couple of pumps in every time you do your oil change, you'll be in great shape.
And remember, check everything again after any prolonged deep water crossings, or after any length of time spend under water, mud, sand, etc. You'll be happy you did.
