Just got a 1998 Chev 3500 Cheyenne 1 ton with a 350 engine. Motor was replaced about 5 years ago with a brand new crate motor from GM. Original motor failed due to leaking intake manifold gasket. The present motor also has the same problem-antifreeze in the crankcase, also attributed to leaking intake manifold gasket. What years did this problem start and when did it end? The local rebuilder advises me that this was a common problem. Does anyone know if this a machining error or poor gasket on the part of GM? Apparently there is a replacement gasket that solves this mess. I don't have the motor out yet and will have to wait for the climate to warm up before I pull the engine. Cheers, Old Iron nut. PS. Truck has low mileage.