The thing is.... everyone I've talked to locally who has experienced this problem complains about a creaking "feeling" in the wheel, kinda like a wood peg in a wood hole. Full-size GM cars AND trucks seem to experience this problem. We have about 5 full-size, late model GM'* in the family. Every one has the problem. No clunking, just an annoying creaking and bind feeling. I'm on my second "creaker".
I can see how a clunk might result from inadequately lubed splines, not from the universal on the top of the assembly. Lubing will help the spline slippage out a bit (a very little bit) but it should do nothing if the creaking and binding is coming from the universal joint. I believe there are many of us with the creaking rather than the clunking problem. (As an aside, my experience has been that a clunk when turning the steering wheel while the car is stationary is caused by a binding McPherson strut upper bearing).
When I pulled my second "month old" replacement I found the splines slip up and down as slick as snot on a doorknob. Well lubed me thinks. When I rotated the universal it was very tight and I did feel kind of a creaking and binding in the joint. Of course there is no good way to grease those u-joints because you can not disassemble them.
Shame on whoever designed, formed and assembled that crap device.