The PCV system tries to separate oil from the engine blowby and send the results to the intake system to be re-combusted or burned.
PCV systems in many older cars are easy to get to and clean or replace, the BMW is a bit more difficult but should be cleaned every few years.
That said, a little oil in the intake trac is perhaps not so rare, especially in older cars that are perhaps not driven as much as newer ones.
I would not worry about it too much and perhaps would try to service the PCV system.