Have the fluid changed. Sure, go to the dealership first for peace of mind, but if they insist that it is a lifetime fluid and whatnot, then take it to a trustworthy independent shop and he them do it.
I don't see why it wouldn't be DIY, but since it is something you don't do very often, I figure it is worth just paying to have it done.
Also, you can change your shifter bushings first. This is easier, probably will cost less, and may even be the culprit. You can get a kit from pelicanparts with all the bushings for your car:
http://www.pelicanparts.com/bmw/cata..._pg1.htm#item1