I wouldn't mess with the fixed cup unless I had to.

After removing the adjustable cup (non drive side), the spindle and the bearings, clean the drive side cup (with solvent and rag) in place through the shell and look and feel if there is pitting in that cup. study the bearing surfaces and balls and replace if there is pitting or discoloration then slap it all back together with fresh grease and adjust to make those bearings happy (no play, no drag). The adjustment works best if you finger tighten the adjustable cup til it stops then finger tighten the locknut til it stops and then use tools to back the adjustable cup into the locknut.