I too have a 318is (M42) and have been using GC (which I really like although I still need to determine where some oil is leaking). I recently purchased some Pentosin Pentosynth 5W40 just to compare. They are somewhat similar oils although I don't know what the base stock is of the Pentosin Pentosynth 5W40 other than it is a Group IV or V I believe. The 5W40 is a bit thicker than the 0W30 obviously but they have very similar amounts of calcium, zinc and phosphorous and the Pentosynth has a minor dose of moly.
Your difference between old and new could simply be that, comparing 8,000 miles old oil with new oil. Keep us apprised and I will do the same.
Regards,
Rich