If you haven't done the job already,here are a few tips that might help.
1. Wire brush any exposed threads, then grease them.
2. Starting with the top nut, ease it undone til it starts to get tight, then retighten, regrease and undo. DO NO put too much tension on this nut otherwise the thread on the stud of the hanger breaks off - £100 the pair
3. With the bottom nut, wire brush and grease, then put a ring spanner on the nut and hold the shaft still with a small open-ended spanner on the flats of the shaft. This works until the nut is nearly off, then you need to grip the shock with stillsons for the last bit.
Worked for me. Hope that helps
Dave