My carpets been getting stained on the passenger side, and I couldn't figure out what it was from, so I took the plastic step off and looked under the carpet, there was some residue (looked like oil) all over the place. Does anybody know what this could be from? I checked under the driver side carpet and it was bone dry. The guy that owned the truck before me had the A/C unit replaced, could it be oil left over from when they replaced the oil a/c unit? Just wondering if anyone else has had this problem, cuz I've never seen anything like it before. [2001 f150 4x4 SC 5.4L 105k miles]

 

The a/c system doesn't hold enough oil for the floor to get oily back there. Sniff it, it is either water from a plugged a/c drain or a leaky door or windshield, or antifreeze from a leaky heater core...