Ramon, I'm with Dan on this.

Find out where Nizpro stands first....if they say they'll fix, then get it in writing.

If they don't want a bar of it, get an engineer to strip it.

They blame the fuel system, but you blame the wastegate. Both cause a lean condition of course, so if you can prove the wastegate was faulty, I don't believe they can say a thing about the fuel system.