Burning oil and low mpg
 

V70 2007 D5 185k miles on the clock.
Has been intermittently blowing grey smoke for a few year's, but always passed MOT. Diesel Consumtion over past year sub-30mpg. Oil consumption recently 1lt per 500 miles. When hot on long journey, can hear loud gurgling through expansion tank.

Plastic arm for butterfly flaps failed a few years ago (easy repair). Opened up pipes and they were 50% carbon and oil. Cleaned out as much as possible.

However, still shifts quicker than my 2017 D4 with a new engine!

Been through the threads on here, but remain confused with this particular set of symptoms. Its definitely getting hot but not overheating. The power suggests the rings and guides likely ok. Is the oil coming from the turbo. Some say a dpf full of ash can cause this... but how?

Car is worth its scrap value - too good to scrap, but not sensible to throw money at it. Any thoughts on a diagnostic method through these symptoms?