Well, for a 4000 mile turbo it seems unlikely, but on a fresh engine and the symptoms you've described it cant be much else.

See if you can borrow a turbo just to try and prove the fault, the last thing i want is for you to fork out on a new turbo and have the same fault, but until you try another one you cant get a definite answer.

if/when it comes to buying a new turbo step gap seals are the way forward