Its not totaly unheard of for the pump drive to fail, I doubt the crank is bad unless you or he ran it longer than stated ,with out pulling caps down he won't know, the cranks are heat treated and have a blue tinge anyway.A turbo failure will not make the oil preasure go away . till all the oil in the pan is in the muffler! The puter turbo codes would not be related in to this Failer . The engine would or should have shut down on low oil preasure that would have and should have happend to you at least once on the way to his shop ( Asuming you drove it there).DID IT!??? If so I doubt the crank is bad yet! Just another opinion take the truck out of his shop to a dealer that knows what their doing!The key here is the Unnessary turbo change with out due cause .He should have pulled the sensor and checked the system with a real gauge before doing ANYTHING else, to confirm the problem, Not depend on a computer code for info. Finding the root of the problem first ,when a pump drive fails, usually two things happen no oil preasure and compressor won't pump. Just an opinion