Vanos seal its not about something wrong with the engine. Its more of giving back the power to your engine. Unless your previous owner has change it already.
Like what iceman says look into upgrading the cooling system. most people always tends to neglate that area which is actually the most important area.
Also from combine experience of two identical 328, some of the nuts and bolts might need to check and replaced. especially the bolts holding the oil filter. that is a whole assembly which connects to your tensioner bearing. And it can break due to metal fatigue.
look into replacing the PCV as well. this has 2 hose and grommet in it. should do wonders to your fuel consumption.
Something which my dad explains. Why do you think when they service airplane engine they replace all the bolts and nuts?
cheers