I recently bought a '68 convertible 400/4bbl. It has a very small (about teaspoon overnight) coolant leak that shows up in the depression in front end of valley pan, under the thermostat. (arrow in picture). The amount in this photo is from about a week of sitting. I originally figured it was the thermostat gasket but I replaced that and still leaks. I traced some chalk around the thermostat, coolant temp sensor, and blank plug on the crossover part of the intake manifold and no leak found. It seems to me it must be leaking where the crossover enters the heads and the liquid is settling in this depression.

Now leaks in a 50 year old car are not unusual BUT I am a veterinarian and antifreeze is highly toxic so I'd really like to NOT have to worry about killing someones cat when I stop by with the Firebird!

The car runs well and I have no plans to rebuild it but would it be possible (advisable?) to remove just the intake manifold and replace the gaskets? Is there some other location I should look for a leak? Any other suggestions? Stop leak seems like a bad idea.