Blow by won't put oil in the turbo. If oil is present before the turbo, what is happening is the tappet cover is being pressurised, aka boost is leaking into it, maybe through valve stem seals, and pushing oil out the breather into the intake pipes. If it is only after the turbo the seals in the turbo are gone which is properly more likely. Pretty ceartin Ford don't build there own turbo's so this would be more a manfactures fault, however ford failed to identify it. Hopefully I am overlooking something smaller thoug it does seem like a lemon.