This one is finally sorted so I thought I would post it up in case it helped someone in the future.
Vehicle came in blowing blue smoke out and a horrific noise from the turbo. We removed the boost pipes + the impeller had a load of play + the fan blades were all chewed up, so replaced the turbo.
Road test afterwards noise gone but it kept going into limp giving up code p1125 boost pressure solenoid valve ammount excessive. Also, if you drove it for a while It would blow out the dipstick + lose a load of oil.
A lot of head scratching later and it finally turned out to be a manifold fault. The inlet manifold doubles up as the cam cover and it was putting the boost pressure into the crankcase

hope this helps