It's possible that on your journey the DPF underwent a regeneration and, as apparently happens with this crazy system, put excess unburnt diesel fuel unto the oil sump. That's going to be the only way the sump can fill rather than deplete. If 6.5 l is 75% that would mean the sump holds 8.7 l. Is it that much? You need to drop the level before the crankcase over-pressures due to excess oil. Also I always worry about the lubricating quality of oil diluted 3:1 with diesel. Sorry to be so cheerful.
