I have the exactly the same
problem as you mate, + same model and year motor. Im 99% sure its just oil in the breather system, I took the top intercooler hose off and cleaned out the inlet, It was full of oil, and this clearer it up for a bit, but its gradually coming back due to oil in the intercooler and bottom hoses, which I've yet to clear out.
Before you spend any money I'd take the time cleaning all the breather system out and intercooler hoses etc. I'm sure if you do a search there will be posts how best to do this.
I'd also be interested in how best to do this, + is the only way to complete cure oil in the system, by fitting some sort of catch tank?