I pulled the wheel... seems to be some oil seepage from the axle as I suspected. I cleaned the rim and reinstalled. Will wait another few hundred miles or so and see if it continues. If so, I guess I'll be heading to Ford for a warrantee repair. It's possible that the seepage occured back when the car was still "new" and I just noticed the evidence now... it's somewhat common for new seals to seep a bit until they are broken in. I had a rear rebuilt once on another car, all new seals, etc, one axle seal leaked a small bit for the first 200 miles or so and then was dry from then on. I hope that's the case with the Stang because I sure hate having anyone touch the car, even Ford, even under warrantee. But.... anyone else ever have an axle seal leak problem on a late model GT?