to pud: they have partially blanked of the egr valve using a plate with some holes in it which apparently is an 'official fix' from AR
I do hope that they plan on cleaning out the manifold first and I will certainly ask them to do so with some of the stuff you recommended.
I don't think partially blanking it off is going to do any good, it would be trying to have a bath with the plug partially in. But they are probably limited in what fixes they can apply as a subdivison of the manufacturer, they are quite limited in what modifications they can do to a car that take it away from its original 'type approval' or whatever. If it came from the factory with EGR I don't think they are allowed to remove that function. An independent would just replace the EGR gasket with a bit of steel, or use a bit of coke can at both ends of the pipe. Plenty on here have done so already. The car would still pass MOT emissions as EGR is to reduce NOx emissions, which are not tested at MOT.
I wouldn't have thought they'd clean out the manifold, more than likely if its working just whack it back on. I don't understand it being a non-swirl valve type manifold, I thought all the 16v & 20v had swirl valves, these are what gunk up and cause the engine light to come on anyway. A gunked up and stuck open EGR valve usually just causes a loss of power.
I'd buy a bottle of that Powerboost stuff yourself, its a great little boost for the cars performance, it made a massive difference to my JTD. That had over 100k on the clock when I cleaned out the manifold (rag on a long screwdriver down the throttlebody, to get most of it out, then Powerboost to dissolve what remained), and what I managed to scrape out would have half filled a can of coke. Unbelieveable!
If they haven't taken the manifold off then there would have been no need to disturb the cambelt. Has your car had it changed yet? Whats the age and mileage of the vehicle as it stands now?