Dollar - Oil Leak

Picked up a 2010 Fusion at Detroit Metro Airport from Dollar Rental, for a pre-arranged price of 415.00 plus change. I drove the car for 2 days and noticed two fresh oil spots on the driveway., I checked the engine dipstick and found no oil. I phoned the Dollar customer service desk and was advised NOT TO DRIVE THE VEHICLE, that they would deliver another car to my home.Two hours later another vehicle was delivered to my door on a flatbed tow truck. Twelve days later, I returned the vehicle and was informed that I would be charged for the tow, because their "certified mechanic" did not find anything wrong with the car.
I informed them that I would not pay for the tow. After speaking with "Dan" in Tulsa Oklahoma, I was again informed that the fee for towing would be my responsibility. Right now, I have informed my credit card bank that I will not pay the extra charge, the taxes and fees associated with the tow. Will I rent another car from them???

Did the tow truck driver check the oil dipstick when he arrived?

You should not have signed the credit card slip if it had the tow charge figured into the total.
(or struck out your signature if they had you sign it first when the slip was still blank).