@LongJon:
I used to be an engineer at EK. They had a couple of old 777s, MIKE series, where they wanted us to do a complete re-rig of ALL the flight controls.
Directive was not just to get the values within AMM tolerances, but to rig everything as perfect as was possible. And we did... and apparently they got somewhere between 1% and 2% better fuel burn than before.
Mind you... those two airframes were singled out - or doubled out
- for poor fuel consumption anyway.
So it is possible for an airframe to go in for a major check, and have everything re-rigged, (not just flight controls, but doors too... pax, cargo, gear) AND the airframe polished back to it's factory shine, AND the engines washed, and you could get a -ve perf factor.
LOL! Dunno why, but the term cougar-town comes to mind! he he he...