Better proof is BMW TIS says to not grease; only clean.

34 21 812 Overhauling left or right rear brake caliper (brake caliper removed)

Special tools required:

34 1 132
Note:
Use repair kit,

refer to BMW Parts Service.


Take off plastic caps (1).

Unscrew guide screws (2).

Installation:
Only clean guide screws; do not grease. Check guide bolts, replace if necessary.

Tightening torque: 34 21 5AZ