so, checking the bmw oem parts list ,front left shock for M sport 704A is part 31316796439, if i cross reference this on auto doc it comes up as 22-183903 which is a bilstein B4 so could replace with this,happy days but it also shows 35-170631 whic his the b6, so am i correct in thinking i can use the b4 on M sport but if I want firmer i go B6?