I had a similar leak in my new car after the 1K checkup. It was an extremely slow leak which I monitored. It went away after I changed the oil myself at 5K.
In my old car I spilled some oil while refilling the oil, and it later scared the hell out of me when it formed a stain right below the tranny. It took me a minute to remember my spillage and I had to laugh.
Whenever you pull a wheel, take a flashlight and look across the top of the service panel. Any leakage is easily visable and should be dealt with promptly.
2014 RAM 3500 DIESEL 4 X 4
2013 Jeep wrangler
1996 Miata race car