Komatsu D20S-5 main clutch not disengaging

I had recently purchased a D20s track loader from an older man. He said the reason he parked it was because the clutch won’t disengage so when you try to put it in gear while it’s running it won’t go into gear. You can start the machine while it’s in gear and it moves fine but if you hit the clutch nothing happens. I took the inspection plate off and can see the plunger moving toward the clutch. Kinda lost at this point. Thanks