call bmw? they dont need anything remarkably special, you dont have to put in the $10 a liter stuff just cause its a bimmer. if you want to, then by all means. but the stuff on sale at crappy tire will probably work just as well if your not drivin the heck out of it, and its way easier on the pocketbook.
10w30 is a really common weight, tho, for year round.