I used Mobil One Synthetic grease. There are other posts in the forum that discuss lubing the joints, but it's really easy.

There are three spots where there is a nipple or zerk joint that you plug your grease gun into. One on each U Joint and one on the shaft. Park on a level surface and if you can't get to the nipples, move the VX up or down a foot to where the shaft rotates and you can access the nipples.

Just be sure to get a grease gun with flexible tubing because it's hard to get a good angle without it. You can plug into the zerks and squeeze new grease into the joints until the old grease oozes out. Wipe off the excess and you're good to go. But be advised that the one on the shaft takes a while to fill up if it's completely dry as mine was.