Basil - having worked on engines for a rather long time, I can say that they all consume oil, some types rather a lot more than others (GE/CFMI having a poor history in the past). Some of that oil exits the engine via the breather air system and the hot section (never to be seen again), some of it enters the cold section of the engine (some of that air passes via the bleed offtakes, into the ECS, into the cabin and into your lungs). Often oil is consumed at low engine speeds and when engines are cooler - taxi/descent - which could be 45 mins of every flight. If you'd like to come down to the hangars and see how you (and your vast collection of genetically perfect acquaintances) are disposed to exposure to oil fumes we'd love to see you....
I'll get my own coat.