Originally Posted by
operator
It'll most likely be a 4mm or 5mm seat collar he's tightening. In which case, it is definitely possible that it is already damaged from overtorquing. And what #2 said, use carbon assembly paste, in addition to double checking that the post is actually the right size for the bike. e.g. 27.2 and 27.0 looks awfully close.
mis-matched seatpost diameter would be my guess, too. or is there something else, e.g., you are a clyde *and* the allen wrench's handle you are using is only 5mm long off the center?