Originally Posted by WhiteFury
So the question is do I use 5w30 BMW or 0w40 GC?
either one would be fine for your engine. It is highly recommended, though not required (still a debatable topic), to use oil approved by BMW's LL-01 long life standards. Another excellent alternative is Mobil 1 0w40 (also LL-01) which has been used on BMW's by many enthusiasts for years with no problem.
from my local market, walmart has the BEST price on the Mobil 1 0w40. prices are really significantly lower when compared to other retailers like autozone.