1st things first:
Find whats leaking and where it's leaking from....

If the coolant was still almost full, I doubt it was coolant.
Drain EVERYTHING, flush and replace it. Coolant, oil, tranny fluid...
Make sure to drain coolant and oil into clear containers to look for mixture in case it is the HG.
Then start it up and look for leaks. If you don't see any right away, take it for a nice easy drive then park it and let it sit. Check for fresh puddles after a few min.