1999 Pontiac Firebird Coolant leak

I have a question i replaced the coolant bypass elbow that goes to the intake manifold & the tensioner assembly because it was leaking and now my car is still leaking in the same area i was told it could be the lower intake manifold gasket.... ? Is this possible ? It would seem that there would be coolant flowing through my engine if that was the case. there isnt coolant and oil mixing but my radiator is also clogged up with brownish crud i was told this is from dexcool coolant. I just want to know if i need to replace my lower intake manifold gasket and what to do about the brown crud in my radiator.... ?
Thank you !