This is what the gear looks like when the gear eats into the bearing.
The noise will be noticeable on deceleration in say 2nd gear...the noise is bit like a Grrrrrrrrrr,
The easy fix is to get a hardened stainless steel washer machined into the gear to act as a thrust washer on the bearing face.
I had this done for me by a mate and never had a problem again, so much so I had the same issue on a new gearbox that I bought only lasted 80,000km until the bearing went, so I put the old modified gear and bearing into the newer box.
I technically would not have bothered stripping the gearbox unless it makes horrible noises, but while you have it apart you might as well replace the output shaft seal.....make sure you use OEM BMW seals...as they are directional for shaft rotation....I made the mistake of putting non genuine seals in and the box seals leaked a week later....