Update.
The order from SAITO came to £336 for the integrated exhaust manifold, new gasket, and a new rod-end. This included next day delivery from Italy and all Taxes.
I had my local garage fit everything which came to £160 labour, a pretty good rate I think.
So the result, so far so good, I've been driving about for 5 days now, 20 - 30 mile trips here and there no problem, no sticky waste-gate! no limp mode! slightly stronger pull from the engine overall. I have to do a long motorway journey yet, but all signs are that it is fixed.
I have seen the old parts and there is significant wobble in the axle that passes through the turbo exhaust manifold, more pronounced now it is removed. and the rod end connector.. well what was round had become very much oval. In all I'd say this added up to more that 8mm play in what should have been a tight fit. No wonder it was misbehaving.