Oil on rim....should I be concerned

[nellie1289]

Halfway into our trip this weekend and as I was setting up trailer I noticed a little oil on the left front rim of my cougar. I tried to take some pics. It looks like there was some on the inside rim too. I took the best pics I could. I wiped it clean and when I got home tonight I saw it had returned. The other side of coach has no such issues. Should I be concerned ? I was thinking I maybe picked something up from road but am not sure. Wheel rolls fine and no noises.