This is not an official upgrade....I replaced the 4 linear sleeves in the Z axis assembly with 2 double long linear bearings. http://www.vxb.com/page/bearings/PROD/LM/Kit8075
It has been about 4 weeks and 35+ prints, I am having great results. I have no Z axis banding. I still have some stepping, but that is normal. My models have little or no Z axis compression. The installation was fairly easy.
1. remove the 4 screws holing in the guide rod collars. ( on the back)
2. lay the B9 down on it's back.
3. gently push the rods up so there is some room to slide the linear slides out.
4. loosen the bolts holding the linear sleeve clamps and push them out and down the rods.
5. remove the 4 linear sleeves.
6. slide the new linear bearing on the rods, and into place. ( make sure they are the same on each side, I just lined them up with the top)
7. tighten the bolts. ( on the sleeve clamps)
8. slide the rods back in place.
9. put the b9 back on it's feet.
10. replace and tighten the screws on the back.
I clean the rods with alcohol and a paper towel every now and then, and lightly oil with 3-1 oil.
I noticed it doesn't really matter any more if one or all the screws on the Z axis clamps are tightened the same.
Hope this helps!