I thought we needed to lube the stock guide pins too (I've been doing it with every pad swap). But kaiv's answer made me double check my e9X Bentley manual.
It says "Clean brake caliper guide bolts (7mm Allen). Replace ones which are not in perfect condition. Do not grease."
Granted, the calipers referenced in the Bentley are not for the M3, but they are a single piston design so I won't be lubing them anymore.
BTW, the tightening torque is 30 nM (22 ft-lb).