Trucky I made a simple observation on the crude design of the swing arm a few weeks ago and felt severely reprimanded for offering a different opinion.
When newly assembled the inner tubes of the silentbloc bushes are clamped between the frame cheeks, which is a relatively small area to provide resistance to turning. Over time as you have found the spindle and inners seize together and whether by design or accident the inners are now well retained along the length of the spindle and resistance to rotation is now transferred more and more from the small areas on the frame cheeks to the spindle retaining flange and bolt. This seizure is why the spindle won't come out, and if the bushes still offer reasonable resistance to turning and spring back, experience is that they can be left alone.
Cutting through the spindle is the least violent and damaging method of removal. Then there are various tricks on the forum to remove the bushes. Worth getting new ones before you start and checking the length of the inners. Some are made a bit too long. They must meet in the middle and protrude just enough to very closely match the inner cheek distance. Too big, the arm won't fit, too small will draw the frame innwards.
Opinions differ on the final tightening, so I will leave you to consider the options. The two "J's " Pete and the KiWi are all on the money here with some sound advice. Thanks fellas.
Swarfy.