[qcj]

Chester, It could be oil your tires picked up off the highway.  I knew that was not my case because my mud flaps did not have any oil marks on them.  Also both sides of the front of the tow had oil spots of it. It doesn't take much.  I was on the road when I noticed it and drove over 2000 miles with a slight leak.  I did check trans. oil level frequently and it always said OK.  I also had a gal. of transyn with me just in case I ever needed it.