I had a coolant leak on my 2018 Duramax 3500hd. After dropping the transmission and running a pressure test coolant was coming out of a bad casting spot on the engine block. I lost my truck for 3 months while the engine was being replaced. GM didn't cover a rental. They tried to keep it quiet at the dealership. I also run two 2006 Duramax trucks, a 2010 and 2011. Nothing like this before. I'm wondering if there is an issue with manufacturing.