This airgap was on a raw water cooled sbc that is only used in salt water. This is after five years. It never leaked, and I thought it was interesting that most of the decay is towards the upper, dry side of the passage. Probably would of leaked out of the motor before in.

http://i1067.photobucket.com/albums/...8/IMG_2173.jpg
http://i1067.photobucket.com/albums/...8/IMG_2174.jpg

interesting

Probably because there is no passage thru the intake, so when you flushed it could not properly flush this 'dead ended' coolant port.

On the small block chevy you could try the TBI intake gaskets. The rear coolant holes are blocked off other than a little bleed hole you could fill in.

Felpro #MS93317
OEM Performance Replacement Intake Gaskets
•Chevy: 1988-93 305 and 1989-93 350 with TBI

http://www.jegs.com/images/photos/30...75-MS93317.jpg

Those are the front passages to the thermostat housing. I will use those gaskets next time because there was similar decay at the dead ended rear ones too.