Had this problem for quite awhile. The carpet under the mat on the drivers side of my 99 Camry (200k+ mi) is half saturated with some kind of oily residue. It eventually ruined the rubber on the back side of the mat. Have no idea what kind of oil it is. Not losing any clutch oil (it's a 5 speed manual) nor any brake fluid, uses some engine oil but don't think that has anything to do with this. I'm thinking of pulling up the original carpet on the floor and see if there are any signs of anything going on there. Read one thread that said the steering column has some oil in it, just never heard of such a thing. Any help would be greatly appreciated.