Just picked up a new project. 1999 S10 4.3 with only 50k miles. Intake manifold gaskets are shot and oil is leaking out the back of the intake and is in the oil (I'd guess a qt or two of water in the oil). The previous owner changed the WP right before it started leaking and was just tired of messing with it. I'm assuming the dexcool was never changed and he said the heat wasn't working great so I assume heater core is stopped up as well. I'm planning on changing the oil a few times quickly to clear out the milkshake; is that all I need to do? Also the radiator looks pretty rough through the cap but doesn't appear to be leaking should I just go ahead and replace it preventatively, or run a flush though it?