- Castrol does make the dealer 5W30, but it *is not* Syntec 5W30 or Edge 5W30. The latter two oils do not have the shear resistance of the European formulas
- Castrol 0W30 has the proper shear resistance (look for ACEA A3 rating on the bottle) and is not sold in anything other than quart bottles
- Syntec/Edge 5W30 is thinner and less robust than the 0W30 despite what you might think about the retail labelling.
I'm really anal about this stuff. The best widely available cold weather oils that meet BMW requirements are Castrol Syntec 0W30 (must say ACEA A3, European Formula and Made in Germany on the bottle or it isn't the right stuff) and Mobil1 0W40.
The Mobil1 shears down to a 30 weight in a couple thousand miles (shown in my used oil lab reports and dozens of others posted on the 'net) so I've stuck with Syntec 0W30 as my winter oil for years.