I got a non-intrusive fix for the sticky d-pad issue!
It works on my sticky/creaky unit and it will probably work on others.
Use a tiny bit of a silicon (or possibly lithium) based lubricant around the edges of the d-pad. Some research I did suggests that for plastic on plastic friction, synthetic lubricants work best and are generally electrical component safe.
Using a toothpick or paperclip, apply the lubricant to the grooves of the d-pad where it meets the cut-out. Hold the d-pad up, then apply the lubricant around the bottom and edges, than repeat for all directions. Be sure to get some in the grooves around the entire d-pad.
Once done, take a napkin and wipe the excess off. I just put the napkin between my thumb and the d-pad and worked every direction of the d-pad and around the cut-out.
Worked like a charm, though I don't know if I'll have to do this again sometime in the future. It's quick, cheap, easy, and non-intrusive so I don't mind having to do it again.
I can't recommend a particular brand for the job as the particular lubricant I used is apparently used for centrifuges. It said right on the back that it was food-grade and silicon based.