MANN and MAHLE (and a few others) have been supplying Euro manufacturers, including BMW, with their filters (and more) for a very long time. The main differences between and aftermarket filter and one purchased form the stealership are price obviously, and packaging. Trust me, I see it everyday as I'm a parts consultant for another Euro brand dealer....

As for oil, Castrol has deals with a few different makers, so that's what you'll find at the dealerships. For me, I was using Lubro-Moly 5W40 religiously on all my Euros, due to the Castrol 5W30 would lose its viscosity after about 3000kms/1875 miles of my 'spirited' driving style, and the LM would last til even after the 5000kms/3000 miles. I have started using another brand though, Total Quartz Energy 9000 5W40 with the BMW LL-98 rating, which is actually made by Elf, and so far it's been holding up.....