If the seals are stuck (mine tore up, without coming out... acted as though they were welded into the tubes!), you may need to heat the tube with a propane torch, to loosen them. Do NOT overheat the tubes! When putting the new seals in, you may want to lubricate them with a very thick grease, to prevent seizure down the road...
I think the book specifies filling the tubes with Dexron III ATF. The III has been replaced with IV, or V, but they're compatible. If you really want to 'tune' your forks, you can play with expensive fork oils (~$15/quart). ATF is dirt cheap (~$4/quart). If you want to improve your front suspension dramatically, install
Progressive Front Fork Springs (you will want to save up, and replace the rear shocks at the same time... otherwise, you will discover how woefully poor the rear suspension is
). Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII