The forks will need re-sealing as they come out as you take the forks apart.
Rather than simply replacing the oil I strongly suggest that you take the forks to a suspension expert and have him tune them for your weight, this will involve him stripping and re-valving them as well as simply replacing the oil.
One of the first things I did with mine is drop them out and take them to my local suspension expert. (While capable of doing it myself Laurie does a dozen sets of these Showas a week! Why would I bother struggling getting it right when he can look at my great bloated carcass, check the spring rate and shim stacks and know exactly what to do!
While this initial set up will cost you, (I think Laurie charged me something like $250 but that was 'Mate's Rates') if it's right any subsequent re sealing or re oiling should be cheap as chips.
Before I invested in the Matris inserts when Laurie did mine he used 5wt oil and about 50ml less of it, re-shimmed the valving and told me to run the spring preload almost as far up as it would go. The result was a huge improvement over stock. The Matris stuff is simply light years ahead though!
If you turn it into a 'Project' you can whip the shock out as well when you're greasing the linkage and swingarm bearings and get that seen to. It needs re-valving, (Replacing is better!) and a stronger Spring too.