Cummins engines have chromoly piston rings.. one reason for their long life (in addition to the tolerances being loose).. Besides, oil's job is to lubricate the rings, not the fuel's?? I hear about the PSD guys having a problem with "wet stacking" if they let them idle too long, and I've heard about the fuel washing the oil off the cylinder walls and causing wear, but never the other way around? Also, look up the Cummins "centinel".. It takes crank oil and sends it to be burned, replacing it with fresh oil... 500,000 mile oil changes... It won't be legal for much longer, but it still is.