I have just done an oil change on a mercedes benz b150. On receiving the new filter, it consisted of the paper filter, and two rubber o rings.The large o ring was for the filter housing,which i replaced, the smaller diameter o ring,was a mystery. I could not find an old one to take off, and coudnt find an obvious place for the new one.I was doing the job without a workshop manual, so i had nothing to refer to.Is there anyone that can tell me the location of this o ring? ,and how critical is it to be fitted? .Also is there anyone that can tell me where to get a workshop manual for the mercedes benz b150 se ( 2006),or online diagrams. Thankyou.