On investigating my oil loss and on/off boost problem, I have found this.

The separator is full of water, the outlet is full of gunk, and when coasting down a hill and then applying throttle I get a cloud of oily smoke.

The separator is only 10 months old

If coolant level isn't dropping, i wouldn't worry about it.
Looks like you've been doing a lot of short journeys in the colder weather.
(condensation from the wet, cold air)

That's the thing, it only does 20 mile trips. To and from work

So, did you finally found the problem??