Fuel and oil leak

I'm not familiar with the Duramax but I've seen Ford Powerstrokes and larger semi engines develop a fuel leak at the fuel injector "O" rings and diluted the motor oil by 50% by the time we figured it out. We would check the oil before going out to plow snow all night and the oil level was going up, not down. That was diesel fuel getting into the crankcase. Watch your oil pressure and level until it's fixed.

There are bulletins on this from GM. Bulletins are available to the public. It give guidance to the dealer on how to handle this issue.