I'm using 10w fork oil.
I went over to Heyser's at lunch today. The guys were very cool. They actually have a very different way of approaching this fix. They told me that they leave the spring and spacer in the tube w/ the cap on. This puts a load on the damper. Then they simply use an impact gun to loosen the allen bolt. If all they are doing is changing the oil, then they pour it into the allen bolt hole at the bottem of the fork.
Luckly I had the springs and a spacer with me. I reassembled the fork (no oil, though) and put the cap on. They simply hit the allen bolt with the impact gun, and it came right off. When I put it back together, I'll hand tighten the allen bolt, add oil, springs etc, cap it and then use my ratchet to tighten the allen bolt. If everything goes well...I'll be riding my bike TONITE!!!
Smitty
PS. This discussion only applies to 1st gen (pre 2000) bandit 600's. Everyone with a 2nd gen bike will have a different fork build.