If it were stem seals it would smoke all the time, especially on start up, and if its rings then you will get back pressure through the breather into the air box - check the top of the air filter and the hose going into it for oily deposits, if these are clean then the next option is below.

Have you gone to a synthetic or thicker oil recently as this may be why the turbo has started to use oil as its getting past the seals - mobil 1 motorsport 15w50 is very thick at this time of year until fully warmed through and this could be the cause as the shaft may not be floating correctly allowing oil to bypass the seal rings. The 2wd YB in my experience does not seem to like the new Mobil 1 motorport -it makes them rattly and drink oil - its fine in 4x4 but a good mineral oil regularly changed seems best for the 2wd - Valvoline 5w50 mineral oil for turbo engines works well in standard or lightly tuned 2wd engines

Go for the cheap and easy options first - change the oil to a thinner spec and if its still smoking then get a turbo rebuild kit from Danny at rad designs (about £65) its easy to rebuild a turbo especially if you are a mechanic

If both of the above dont solve your problems then its head off time - but at least you have fresh oil and turbo so its not money wasted.