I think I already know the answer to this.
Bought a gt1756 for the pd150 has minimal side to side play and no back and forth. Turbo had little use (apparently) and spun easily.
Installed it and started it up and left idling to get oil through and do leak checks. We're none.
Took it for a small drive and I know its not mapped so the boost would come in a lot later but have it one little boot and had smoke out the back.
Pulled up to the lights and I could see faint smoke coming out the bonnet which stunk of burning oil.
And then starting it to drive home there was thick grey smoke out the back ( burnt oil smell) and when changing gears it would hold the revs.
Now I'm safe to say the turbo is knackered and can query the purchase as they say they had it looked over before they sold it