The housing where your oil filter connects may be cracked, or it may just need a gasket/ o ring kit. I actually leak oil in the exact same place. I need to order a kit to fix it in the Spring. I wouldn't worry about it too much- should be an easy fix. I believe the kit with new seals is less than $40, but don't quote me on that.
I seen a thread a while back and it said you could get the whole rebuild kit straight from Ford for like $38. That was back in the spring though, so IDK if they've been discontinued, but I doubt it.