Was: 96 Chevy Pickup Intake Leak?

Had a Intake manifold leak on my 96 Chevy Pickup with 5.7L. Leaking from
passenger side front. Thanks for all of the help on this so far! When I
pulled the intake, I was surprised to see the 2 intake ports on the front of
the motor on passenger side (2 and 4 maybe, can't remember how Chevy counts
cylinders) had a thich goooy black tar like coating up to 1/8 thick maybe
choking down the ports. Felt gritty and had to dig out with screw driver.
Is this what happens when the Dex-cool comes in contact with gasoline?
What would cause this? Also had some black chunky stuff stuck in the
valley between lifters. The stuff was hard and gritty. Felt like clumps of
sand with oil. There wasn't much of this but I have been using Mobile 1
since the truck had ~20K miles (now has 136K) and was surprised to find goo
and chunky stuff in the motor. I am using K&N filter but will probably go
back to paper.....

Thanks again for any input. Just curious what would cause the goo in the
ports and the gritty stuff in the lifter valley.

bb