96-99 vortec 350s had plastic intake gaskets that fail. Every one of them will fail. The block and heads are iron, the intake is aluminum, different rates of expansion, they chew up the plastic phenolic gasket over time with all the heat cycles. You will notice the smell when the temp outsides fluctuates cold/warm then you won't smell anything during the summer months, then when it starts to get cold it will start to smell again.
The water passages are breaking the intake gasket apart and the pressure from the cooling system is pushing antifreeze out of the gasket. If you do not care of the problem soon you could run the risk of coolant dropping down into the lifter valley / oil pan and spinning a bearing. The cure? Replace the intake gaskets.
If you take a flash light and look under your a/c compressor, alternator, or back behind the block you will most likely see the trail of antifreeze. Most of the time it'll make it's way out the back of the block and down the transmission bellhousing, then drip on the exhaust crossover.
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