I'm at a bit of a loss, its highly unlikely that a slight overfill measured in spoons would start feeding the engine lube to run on, IMO, rule that out.
I would also rule out the leaky injector, if this was a long term problem, the dipstick wouldn't show low, it would show over, as the Jtd doesn't burn oil unless its got a problem.
I can't rule out the turbo, and you need to ask why they think it ain't faulty because:
A) if your dipstick recorded low and there were no leaks, something....such as the turbo...was feeding the engine oil in low quantities in the weeks before.
B) the turbo is in the intake and is the usual culprit for leaking oil mist, then ultimately liquid oil straight to the combustion chamber.
Warranty people wriggling I think. I don't have expert witness PI for road vehicles, but you do need to employ a suitably qualified and insured independent consulting engineer.