As advised, I've just taken the swingarm off my GRiSO to regrease the bearings. I cannot overstate what an extremely good idea this is, particularly if it had been done say, 10,000 miles ago.
As it stands, a mere re-grease won't do the trick. I can't say I wasn't tempted, and packing the rollers with enough grease got rid of most of the graunching, but ultimately, I couldn't bring myself to put a nice shiny new Matris on the bike and not do the bearings.
So, at the risk of sounding a bit gash, would cutting the old races with a Dremel seems like a reasonable way of getting them out? There doesn't seem very good access to the back of the race to drift them out, but I'd love to be told otherwise.