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I'm not a mechanic and put my recently acquired 1990 Corvette in the shop last week. The mechanic (very reputable in the area from what I'm told) just called and said the intake is very pitted and leaking antifreeze. He said the intake will need to be replaced and found one for $600.00.
http://www.ebay.com/itm/89-Corvette-TPI-LOWER-INTAKE-MANIFOLD-91-90-tuned-port-injection-C4-Vette-/221241459881?pt=Motors_Car_Truck_Parts_Accessories&hash=item338304c4a9&vxp=mtr
Any other questions
Just an oh by the way, do not use any sealant that smells like ammonia on aluminum. That sealant, blue, black, green, red, eat aluminum, and people seem to gravitate towards it .
The best sealants are the ones that have a rather dull smell, and give a faint odor of solvent. The previous owner probably bought a tube of the blue stuff and sealed up the intake with it.