The excess drained out of the overflow until it was down to the level it should be...
You must have a hole in the heater core. There is an old remedy my dad used and that was putting ground black pepper in the radiator. The pepper circulates and the water pushes it into the hole if its not too large.
i have this car i didnt know where it was in till recently the dipstick for the transmission is on the drivers side right under where the brake fluid resovour is look straight down and where the transmission shifter cables enter the transmission its a red plug that's ur dipstick. hope u find it cuz it kill me lol hard time finding it
If it is on going from neutral to any forward gear, bleed the lower resovoir. On sitting for a winter of even a month on hot dry weather will cause air to leak in. If it is on fast shift to third the fluid return hose has a metering block in it to slow down shifts. This can be reamed out. After a fast first to second the second to third doesn't have enough fluid back in the upper resovour and locks you out. A good Corvette mechanic could help you here or look to the internet and somewhere the ream out is detailed. While you are at it use a turkey baster and pump out the upper and depress pedal and give it 3 mins to fill then re pump out with baster. Use STP Synthetic power steering fluid DOT 4 or better.