If the post doesn't move you're good to go.
Your beam wrench has what range? Common beam wrenches have a range of 250 ft-lb or more. Your spec is only about 5 ft--lb, and wrenches are generally considered inaccurate in the bottom 10% of their ranges.
Btw, the abbreviation is in-lb, not in-lbf (I presume the 'lbf' is supposed to stand for pound-feet, but the "feet" is out of place).
His link to the TW-1 shows it is 0-7 Nm or 0-60 inch lbs.
jeanluc - put some tape on the seatpost with a small gap between the tape and the clamp, and see if it slips at all on the next few rides.
I have a tube of
tacx assembly compound. It's not really grease, just a very fine plastic grit in a gel base. It works great on the seatpost.