Q: I went to get gas and when I opened my gas cap there was a red puddle of liquid at the entrance to the gas tank.

I can’t think of another explanation. That kind of vandalism is not uncommon. You need to have a sample taken from the fuel and checked for contaminants. It might be necessary to drain the fuel tank and clean it out. Since the fuel pump lives in the tank, it may have to be replaced as well. You might be able to get some help from your insurance company if it turns out that someone has tampered with your car. It would be best for you not to drive the car until you can get this sorted out. Contact Your Mechanic to have a technician come out to your home or office to check out your Cadillac and let you know what steps need to be taken.