Like with most others, Impact gun helps for the bottom bolt; You can make your own “seal driver” from the old seal/bits of drain pipe/ spent silicone sealant cartridge / even some stiff cardboard and a jubilee clip. If there is minor pitting/dings on the stanchions causing minor leaks, you can clean them then use superglue to fill them in and a sharp scalpel to smooth them down. I used plastic from a sparkling water bottle made into a tool to try to clean grit from old seals and eventually to drive new seals down the stanchion to avoid nicking them on corrosion/ding and making them leak again.
Oh, while you got them off, May as well get a rattle-can of smooth silver hamerite to tidy up the bottoms as they have inevitably corroded after 20 years.
hamerite works fine for the waterpump cover too. I never saw one where the paint is not ‘orrible there. Hamerite is a decent match but takes forever to cure so extra care on reassembly red’d.
Inspect the bottoms, near the axle-holes for cracks carefully and do the axle back up / torque properly. I believe there was a batch where they were prone to braking off. Nasty, that. You can have a look
here [ good site, that for most 650gs stuff.]
Good luck.