Expect it to be corroded in place requiring lots of penetrating oil. If you are going to replace your prop shaft seals in the bearing carrier then you could use heat to assist in the removal. If push comes to shove expect to have to make cuts in the spanner nut and bring it out in pieces. Chasing the threads with a wire brush....the round ones, roughly an inch in diameter, with the wire and plastic handle Harbor Freight carries them works great. Then a new nut and blue thread sealer (HF has that too) which lubricates upon reassembly, helps to prevent corrosion, and locks the nut from backing out.
