I just replaced my 4x4 1995 NV3500 5 speed manual trans' clutch pack.. Thank God a friend let me borrow his commercial transmission jack. It worked great for a couple of months and then no clutch engagement and I had to be towed home. Clutch peddle resistance changed to very little at all. I suspect clutch master cylinder internal o rings failed, since there is no brake fluid leakage. However, I jacked up truck and open the slave cylinder's inspection cap and notice the castle nut hanging just inside and covered in black grease. I am the 3rd owner of truck. Nut appears to be 5/16 threads or metric??? I believe it was used to attach and position fork while assembling transmission back onto flywheel. I don't remember installing it. It may have loosened and fallen to restricted fork movement? Any ideas????? See attached photos. THX!