TURBO FAILURE, something else wrong

[michaelcngm]

I'm in rather desperate need of ideas! Just before Xmas on a 45-mile return trip, I started to hear the turbo. It wasn't loud, but clearly there unlike normal. At Xmas, we set of on a journey with our fingers crossed, but about 35 miles down the M74, going up an uphill stretch, the turbo gave up completely. We struggled on a bit further, but were soon leaving a smoke trail, and pulled off to get recovered. The car's been in getting the turbo replaced, but the garage doing the work (they're recommended fitters for The Turbo Guy in Glasgow) cannot figure out what's causing a continuing major problem. What appears to be happening is that as the engine warms up,a large amount of oil is getting into the engine, mainly to cylinder no 4, then getting out down the exhaust. They found that the DPF had become blocked, which may have happened with the turbo failure, as the car was running fine until it failed. The DPF has been cleaned, the replacement turbo has been thoroughly checked out, and the other oil feed and drain pipes replaced or cleaned.
The garage guys are running out of ideas, and are not prepared to dismantle the engine themselves to investigate any further.
Any experience of this failure anyone? All suggestions welcome!!