OE oil is blended for BMW by Castrol but isn't an oil you can buy other than through the dealer.

BMW 5w-30 has worked well for me on multiple six cylinder BMW engines. Stands up to 24,000 km changes just fine.

Some would say the issue is the eight cylinder valve stem seals, not the oil. Some owners are compensating by using a heavier oil, with less lubrication/higher friction, but also more resistance to passing by the seals.

__________________
2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue