For the last couple of months my 2500HD with 150,000 miles on it blew white smoke a little at idle and after a stop. Then!! while I was on the Freeway the truck started to tick. I would slow down or speed up and so would the tick. I pulled off the fwy and White smoke started to pour out of the tail pipe and out of the engine compartment. I could also smell a strong odor of fuel. I towed the truck to a Diesel Mechanic and was told that one of the cylinders was flushed out and I needed a new engine, to the tune of $17K plus. I have what appears to be fuel in the crankcase. The truck still starts right up and I turn it right off. What happened? What to do?