My 2006 Impala SS has 97000 K and while doing a cooling system flush, I encountered soot or a darkish sludge in the bottom of the reservoir tank. I'm concerned that is may be evidence of an intake manifold gasket leak. Any advice for me from anyone? Any websites I can visit which has any history on this issue. Hurry please, as the car is in for other major warranty work right now.

 

Welcome to the forum,
I suspect its more likely just normal build up probably from normal corrosion form the dis-similar metals of aluminum and iron and the acidic nature of old coolant and maybe a tiny bit of deteriorated rubber from hoses and maybe some plan ick growing from the wet warm environment...
Unless you are seeing a consumption of fluid I wouldn't be to worried, I would perform a thorough flush and see what comes back... my .2¢

 

Thanks for your thoughts. I didn't mention that I was down 3 litres of coolant as well. The cause was the water pump, has been replaced. I'm having the cooling system flushed and the tank removed and blown clean, so I can follow up on any further discolouring.