I removed my seal holders with a 'Stilson' pipe wrench - it marked the holders but as I was replacing them anyhow it didn't matter, you need to grip the holders near to the bottom or as you've found, they will distort. There is a recommended special tool, (sort of a tubular peg spanner), which locates in the base of the holder, (look down inside with a torch and you'll see two slots for this. I didn't buy the tool as I don't see any requirement to over tighten the seal holders on installation.
Once you have unscrewed the seal holders they will slide up the stanchion about 6 inches before the seals become stuck on the increasing stanchion diameter. At this point look down into the slider and you'll see a wire circlip, remove this and then pull the stanchion out of the slider, you may need to extend it a few times against the upper bearing and removing the drain screw facilitates this.
With the stanchion assy out of the slider you can remove the bottom nut followed by the washer, bottom and top bearings, possibly a shim or two from the top of the upper bearing, circlip and oil seal holder.