My two cents....
There seems to be a big concern on turbo failure and the risks of buying an older turbo diesel because if this unknown timebomb....But the concern deserve the attention it has?
My turbo on my 320d went at about 120000kms. I pulled it out, reconditioned it at an engineer, and put it back myself, Cost about R4500. Ok to be fair you will pay more if you don't do the work yourself
Then later my alternator went, and the a new one cost over R7500.
On my other e90 the waterpump was now replaced and I paid almost R10000.
So my point is both these other items that can happen cost more or the same as a turbo.