The pump appears by all accounts to have a sticky timing piston. The issue has been going on for awhile before and after a blown head gasket and complete head replacement. The symptoms are enough blue smoke at idle to rule out all bad timings and some lurching at low speeds. It's fuel not oil for sure. The proof is in the injectors which are taking on carbon at a break neck pace. I rebuilt them just recently with new nozzles and popped them to spec but it didn't solve the problem.

Basically my question is how much can be done in the way of cleaning that piston and the bore? And if it's just stuck but not warped can it be freed in that case? In general I would rebuild this thing myself before sending it back to the snobbiest turbo shop in the country where it's been rebuilt twice already. I would disassemble it myself, clean it and then take it to the shop and have them bore it out and refit the piston and put it back together.

Clearly this is about as tough as it gets with injection pumps but it's also 1 of the more common problems and I did read the thread on the VP44 pumps which mentions the same thing. In this case there's no leaking so I don't think it's battered the housing too badly.