I bought a used 95 KDX 200 several months ago and I don't think the brake fluid or fork oil have ever been changed. Everything currently works fine. Is there any reason to change just because it is old even though it works fine? The shop manual makes the fork oil change look like it is fairly time consuming and you need a few special tools? Any advice on changing the fork oil would be appreciated, and also what oil to use and brake fluid to use. Thank for the help.
Changing the fork oil isn't that bad. You can buy a guage or make one, or use a ruler (in mm) and measure from the top of the fork so you get them even. I used Mobil 1 ATF (which is about equal to 7wt vs 5wt fork oil).
There are photos on my site but I also changed the springs.
I think there is some interval at which you should change brake fluid, but if it aint broke don't fix it.