Clearly this is an issue linked to the original rebuild and really has nothing to do with anything done thereafter by said reputable workshop. This is a classic case of dealer and engine rebuilder handballing.
What you need to do is get a written report from the reputable workshop describing the work they did on the car and the problems they observed....eg the blocked AVCS was obviously as a result of the engine rebuild...the bad hoses were probably something the engine rebuilder wouldn't have worried about - they were probably on a tight budget from the dealer.
Stories like this sadden me since you bought the car in good faith but the dealer has obviously tried to rectify it as cheaply as possible and there have been mistakes made...they are now not taking responsibility since it has been to another (albeit reputable specialist) workshop. And this is all from no fault of yours.
Good luck...

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