i should have been clearer ! the torque spec is 13.5 N*m. i torqued it to that value initially, and after a few rides it slipped literally all the way to the front of the rail, into the angled part.

torqued it a bit more, approx 15 N*m, and after a few rides it slipped back from the midpoint of the rough area to the position shown above.

i'll try some carbon paste. most of my tools are leftover from car wrenching days, so my torque wrench is a little vague on the difference between say 13.5 and 15...