I've been trying to get up ATF from a concrete floor indoors. Nothing has worked so far. I had kitty litter on it, but it sat for years. I've hit it with mineral spirits, solvents such as acetone, brake cleaner, even Lime-Away. I even hit it with a propane torch. All helped somewhat, but it keeps oozing up out of the slab. It's a smooth steel trowel finish, which probably doesn't help. I'd like to finish the floor, but the dark stains will show if I use a concrete stain, and I'm afraid paint won't bond well in those areas.
I'm convinced the automatic transmissions manufacture fluid as they sit. I tilted the culprit all different ways and let it drain, but it still oozed a puddle. Now I moved it into my shop, and fluid is still coming out of it!