First, remove the rotor and hub unit off the spindle. Clean ALL grease from the parts, including the spindle, then dry. Your workspace should be clean and grit-free to handle the bearings one they're clean.
Inspect the bearings. Raceway surfaces should be free of color from heat, no nicks or dents, and should still have some honing marks visible. They should be close to perfect.
When regreasing, pack the taper roller by placing a dollop of grease in the palm of one hand, and scraping it into the spaces between the rollers until full. Butter all the hub interior cavity surfaces with grease. Place both inner and outer raceway into the hub and add grease to the sides. Install grease seal.
Make sure you use a quality grease, typically a lithium-based NLGI 2 grease with EP additives for high temperature applications. Don't go too happy with the grease, since too much will reduce thermal transfer properties, thus reducing life of the grease and bearing.
Once everything is assembled back on the spindle, rotate the hub while wrenching down on the hub nut. This'll seat the components and squeeze the excess grease from the bearing running surfaces. Wrench down until it's difficult to turn the hub. Then back off the hub nut until slack.
Set the hub nut for proper axial play according to specifications. It's best to use a dial gauge for this. If you go by feel, as some of us do, gingerly tighten the hub nut until axial play disappears - no more. You have to develop a good feel for this. You can't just wrench the nut down, or else you're sure to get early failure.
95 E320 Cabriolet, 131K