Crap. Starting to pi$$ me off, too

First, you're right: never overtighten the post clamp. Seatposts only need enough torque on the clamp to stop you from pushing the seat clockwise/counter-clockwise *with one hand*. That's not much.

Second, you mentioned that you overtightened one bolt once. Possible that you cracked the top of the tube when you dented the other post?? Get a real good look, maybe with a bright light and a magnifier (or any eyes better than mine!). Grease isn't *going* anywhere once you put it in, so if it worked, it should continue to work . . . unless only a touch of it is getting into the noisy bits. That's why I'm thinking small crack (again: ?)

Third, hate to say "LBS" on this one, but . . . you . . . could....

Fourth, you say you're sure it's not the rails, but have you swapped for another saddle, greased and reinstalled those fasteners just to be sure?

Fifth, have you removed and cleaned (WD-40 and a rag) the two seatpost binder bolts, then greased them with a good quality grease prior to reinstallation (shoulda' thoughta' that one before )

Sixth, [this space left intentionally blank]

Back to you....