I have had this car for a few years 1987 740 Turbo in Australia. It now has 2360000 on the clock. I had a major overhaul at 200,000 . Apparently.
The mechanic reckons I should get rid of it!

On boost the Turbo just delivers no power. In fact it has no acceleration

I have had a good read here. and am now at a loss..

The plugs were wrong. So I changed them. However they were a nice grey and were probably OK.
The turbo had hissing coming from a tube. I have replaced any I suspect have a crack or a hiss.

There is no pressure on the oil cap.
No oil in the water
There is some back pressure on the fuel cap

It stared after a service. Someone knocked what I think is a breather tube [It Runs from the Turbo inlet] to near the manifold It is about a 1" pipe. There is a plastic joiner with a small Α/8] T piece going to the manifold. This was snapped. For now I have blocked the tube and taped up the other end !

Tubos are new to me Obviously! i have rebuilt a Renault 12. But since this I have let someone else look after my car.
any help or clues gratefully received
thanks in advance
robert