Overboost limp mode?

[TDWEYI]

Morning gents
The wagon has developed over boost limp again, its only eighteen months since i totally stripped the turbo and cleaned the V V mech.
These pd 130 lumps don't suit the about town 30 mph driving week in week out, which to be fair is most of its life.
Im considering some millers additive as the thought of removing the turbo again isn't good.
Switching off and back on the boost is back, I've red lined it in every gear and horsed it up the local bypass, it pulls like a train, I got some smoke out the back under high load but nowt major.
Your thoughts gents would be much appreciated.