Carbon assembly paste on most things, even places like seat rails.
I did have a set of Guide RSC's that with the clamp fully tightened it maxed out and wouldnt get a grip on the bars, I used a needle file on one of the surfaces to take a bees dick off, was able to torque them properly after that.
A step up from normal assembly paste is effetto Mariposa Carbo Grip, this stuff is sticky and nearly likened to an adhesive. This was the stuff that fixed the massive issues with the first Niner Eccentric BB's creaking but semi dries as a glue, also great for problematic pressfit BB's.