i just changed the fork oil (and brake fluid) on my "new", 16 year-old KLR. (with only 6kmi)
PO had NEVER done it
i'm planning on installing cartridge emulators in a short time, so i just drained, flushed with a small amount of fresh oil and filled... more complete service when i tear them down later.
the old oil looked like somone let charcoal briquetes disolve in water... NASTY.