We have been given a Bosch rotrak 40 lawnmower by our neighbour .Who has moved into an apartment .Blade is blunt so i bought a replacement .But the securing nut is stuck fast .Three days of 3-1 oil has not unstuck it .So just given it a splashing of gt 85 .Will leave it for a week .If it does not budge ,what can i do to help release it .Or i shall take it to a repairer to see if they can undo it .Any ideas ?