Jason,
I have the same problem on my truck. I went to the local hardware store and picked up a small piece of that hobby type brass tubing that is about the size of the threads on a zerk fitting. I cut it to about 1 1/2"- 2" then forced a zerk fitting into the tube. If I hold the other end tightly against the fitting on the U joint I can grease the joint.
Works for me.
Jim
