With one bike of mine, I ended up hacksawing through the spindle (a tube in my case, crossover rear brake) between the end of the s/a and the frame plate at one end in order to remove the s/a from the frame. No matter what I tried, I could not move the spindle in the s/a 'in situ'.
Once out of the frame I burnt out the old rubbers using a gas torch and then slotted the silentbloc outer tubes with a sharp/new hacksaw blade, before collapsing them using a hardened ground spike (and hammer, of course).
An entertaining morning altogether!