Could it really be that your lube took care of your ongoing problem. You have to wonder why the dealer couldn't have done that?!
Your dealer must have chamfered your rear pads the first time you took it in with the problem. The dealer who did that to mine (which I think fixed my problem) told me he did it (chamfer) because it would help keep the groan/grind away since I brake so much on windy, hilly roads. I don't think he would have explained it to me if my pads were already cut that way.
Anyways ...
fourfourto, for getting to the bottom of your problem and fixing it. I hope you've heard your final groan/grind. If possible, try not to make aggressive stops .. ease into it as best you can. Good luck! Keep us updated if the groan starts up again.