When I pulled the ZX forks apart they were full of rust in the bottom of the dampners. I had to replace both forks.
A few tips if you want to build them up a bit... I cut two spacers out of stainless pipe that fit into the tubes on top of the springs. (10mm spacers) That pre loads them a bit more. I also drilled the dampners to 1/8" to quicken the response. It's been awhile but I think it was 8wt oil I used.
All that stuff made them stiffer, and faster. They will actually follow a washboard road now where before they would collapse further on each bump till you slowed down, and let them re-bound.