I removed the manifold assy. and found that it had warped as you said Kev. The centre area of the rocker box was distorted upwards relieving the pressure on the centre gasket, this allowed boost pressure to leak into the rocker box and forced oil out of the rocker box and filled up the centre 2 injector reccesses and surrounding area. Oil was probably running down the inlet ports after switching off which caused the blue smoke on start up.
As you said Kev, not as involved as it looks.
Roadtest after repair and the performance was improved and got upto 2.5 bar boost as opposed to 1.7 previously.

Regards, Martin.