If the oil is grey it usually means there's water in it. You should change the oil right away, try to ride it for a bit then change it again. If it turns grey again then it's possible you have some leaking seals. For the water to get into your crank case it would have to leak through the head gasket into your crank case then through the right side crank seal into your case. If you measured the thickness of all your clutch rings and they are in spec then your clutch is good and needs to be adjusted. If they are worn out then the clutch should disengage just fine and slip rather than jump when you put it in gear. The only thing that would cause it to jump is being improperly adjusted. Screw the adjuster on the clutch lever in until the cable has no play, if it still jumps you could have a worn out clutch rod (the rod that separates the clutch disks running through the crankcase), or the lever on the crank case which operates the clutch rod. Do you have a manual? If not, search you tube for a video, you might get lucky and find a good visual.