I don't know as much as Bob Mc carthy on this but after speaking with Nico it seem the were disqualified after leading from start to finish because:
They were only running on 5 pistons for the last hour or so.
Work that out.
They led for the first 8 hours & then from the 15th to the 22th hour & then finishing 4th.
From what I gathered they were dq'd to 7th for dangerous driving. Never heard the piston thing though.
However right after Rouen on the Ghostbuster website they were real pissed, but my dutch isn't so good, something about those damn french, this was later removed...