There is really no way for fluid to escape a transmission except past seals and out the dip-stick tube…I had a Malibu that did that once, fluid poured out of the front seal of the transmission for about a minute then it quit. But over time, the leaking got worse and I had to rebuild the tranny…
To remove the mess from concrete, spread the cheapest cat litter you can find on it then work it into the cement with hard-soled shoes. Really grind it in. Then sweep it up. Next, sprinkle laundry or dishwasher detergent over the spot and spray it with water (lightly). Work it in with a broom and let it sit for 1/2 hour and hose it off…Repeat if necessary. As for the gravel, you might have to just spread more gravel on top. Over time, it will “blend in”…