iv heard of that causing the manifold to crack around 120k miles, Due to that bug. My 99 does it too, I'm not really that worried about it. If nothing else it will give me the excuse to get some nice headers eventually
All that is is the condensation from the AC running dripping down and landing on your headers. It forms from the AC running and being colder than the air around it causing water to form and collect. When you are finished driving, it continues to drip and it sounds like it is located right above your headers.
Transitioning from hot to cold at a rapid pace (Your hot headers being unintentionally cooled by the condensation dripping) can cause cracks in the metal over a long period of time. But I'm sure you won't have a problem running your AC like you have been and it dripping on the headers, causing them to crack. And like you said, if it happens, it gives you a reason for new, better headers. If anything, my younger brother had the same issue and he made himself a steel run-off, like gutters, that collects the condensation and runs it off to the side where it won't hit the headers. I think it was too much work for a minor issue.
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