Retailers usually list the BMW part number as just a reference, so it can leads back to many different OEM and aftermarket choices. Rarely will the sell the OE part which is attached to the part number. That's usually just dealers or if you specifically ask for the OE part.
This spark plug (253) does not have a brand name attached to it in the ETK, so you could probably get either brand if purchased at the dealer.
EDIT: When I plug that part # into Tischer it lists each application line-by-line. They include both NGK and Bosch in there. My guess is it would be a crap-shoot.
If you really want NGK, AutohausAZ has them for $14.17 each.
Last edited by CirrusSR22; 04-20-2011 at 06:49 PM.