I don't think the rotary screen on my JD 4420 is working like it should. Seems to gather corn leaves and chaff on the outer screen. The book talks about an adjustment between the rotary knife and stationary knife. Book mentions loosening two bolts for adjustment. Still not clear. I have never done anything to change the adjustment. It does look to be wider than the 1/16 to 1/8 inch spacing between the two as recommended in the owners manual. Seal between the door where it sucks chaff and the fan compartment is in very poor shape. I am assuming that this seal is very important??? Any ideas to make it work like it should?? Thanks.