I've got a 1990 ZX11. After a couple weeks the clutch lever gets spongy. I've rebuilt the clutch master cylinder, replaced the clutch line with a steel braided line and no difference. I just ordered a new piston seal for the slave cylinder but I have a suspicion it's the master cylinder itself. A couple years ago I went through the same thing with the front brakes, I measured the inside of the master cylinder bore only to find the bore I/D was wider in the first 1/2 inch. I think the same thing is happening in the clutch master cylinder. Anyone else go through the same thing?