Sounds to me like your cranck case breather it venting oil vapour into you filter then the vapour is condensing again then settling somwhere in the filter and leaking out, nothing to worry about just find the leak and try to stop it as all oil vapour should be sucked back in to be burnt off during combustion.
If there is an an exessive amount of oil there is the possibility you may have over filled the engine with oil, when you do this the oil normaly finds the fastest way out which is normaly the dipstick tube or the cranck case breather, if this is the case, drain it recheck the level clean up as much of the leak as you can make sure the breather is working correctly and free from blockages and in time the rest of the leak you cant clean up will filter through and be burnt off.