I would check the entire brake system for leakage, if the brake fluid isn't low, the only other place for oil to come from, is the fork drain plugs .
They should have a copper or aluminum crush washer / seal on each drain plug, they sit in a machined 'well', if they are outside of this machined area, they need to be removed and filed down to fit the machined area .
The threads in the fork tube strip out quite easily, so be mindful of this if you attempt to tighten the drain plug !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!