I see your predicament and hope it gets sorted soon.
I would hope there is no excessive soot as this is what the DPF is supposed to catch.
What oil is being used? This does have a slight bearing on engine performance and thus burn efficiency and as you rightfully point out constant regens can compromise engine oil quality too.
There is obviously something wrong here one way or another and as you say your running out of warranty mileage. Can you not arrange with dealer to obtain a courtesy car so they can have yours and get to the bottom of the problem once and for all?
Good luck!
