Thank you for taking the time to give us an in-depth answer V8volvo.
I have to say the fuel injectors are the only thing left on my list of big maintenance jobs that I haven't yet done since buying the car so if in getting them rebuilt sorts the issue I would be happy.
In terms of the turbo I have run a homemade catch can for some time and having recently pulled the outlet pipe off for inspection the vapour is oil free at least at idle and under no load throttle. There is some end play on the turbo intake side when cold but I keep forgetting to check when warm as from what I gather it is better to check this when warm due to the expansion of the metal. It would be worth mentioning that this turbo is not an original it's an exchange unit from a very highly respected company, however from what you said about it being rare for a D24 turbo to fail, it might be worth changing it back to an original unit. I have had very bad experience with cheap turbos in the past so my suspicion keeps leading me back to it (despite costing over £300 for the exchange unit). Following this trail of thought the one I sent off to get exchanged that was passing oil when I got the car was also not an original but was a remanufactured Garrett unit.
In regards to an internal issue, one of my recent maintenance tasks was the valve shims and almost all the intake side had no clearance before I changed the shims so perhaps this could have had an effect on the valve stem seals?
Finally I have no EGR on this engine as it is an early type with mechanical lifters and such.
I hope this gives you a bit more information and I will try removing the exhaust for evidence of oil on that side of the turbo.
For interest here's the company I used for the exchange unit:
http://www.universal-turbos.com/
And I've attached some pictures one is the turbo I took off the car (red tag) the other is the exchange unit.
Thanks again for your help