1. The N52 engines until the revision in 2009 have a known problems with the valve tick on idle.There are a few fixes for that,replacing the lifters,rockers and sometimes the head.My 06 530xit with 170 k miles has a minor tick when it is driven on short distances or after it idles for a prolonged periods.However I would not be bothered unless it gets really loud and annoying.I just stick with Castrol Syntec 5w30 oil,and make sure the engine gets over 5000 rpm at least a few times a day.