They are steel and fiber plates stacked like most any MX clutch.
First thing is dont use that oil. 10-30 or 10-40 is specified. The heavier oil is NOT needed. You may be making things worst since the heavier oil will flow slower and may be the cause of your problems. Really though, if you want to run a better fluid, get some honda HP tranny fluid. Also the redline synthetic ATF seems the same. Seems that a lot of people have had good luck with the Type F atf also in the KDX trannies.
Second, inspect the clutch. I am thinking you are going to find a lot of worn and grooved disc in there. Replace and repair what you need. Be sure to buy a new clutch cable also and adjust the play properly.