Just to start off, I drive a n54 transmission but I'll post it here since it is a general MT question.
What is the reason for a particular gear to go? I do noticed sometimes that when I go into 3rd, it seems to grind ever so slightly (not every time) but I always thought maybe I did not clutch in properly. And this problem is noticed shifting up from 2nd. I never have this slight grind in any other gear btw.
When I am cruising in 6th, I would sometimes drop to 3rd (and properly rev-matched) if I want to get going in a hurry. Would this cause the problem that I have in 3rd? I thought BMW tranny are reasonably robust in that regard.
Is my 3rd going? If it is, would the dealer cover it as in the OP's case?