took my FBM out today and cut some limbs off of an old apple tree, and i have to say this thing can really chop. here's the problem i can't get the sap and wood fiber off of the knife. i've tried WD-40 and 3-n-1 oil and lighter fluid but nothing will take it off. i don't want to use steel wool for fear that it will take off the coating. i am open to any suggestions.