90 predator 2004 locks up ??

Hi everyone I’m new to this site was looking for some answers for a problem I’m having with a 90 predator and stumbled across this website so I decided to join . I have six quads 3-90s 1-50 1-500 scrambler 1-250 trail blazer( The 50 was for my youngest son which has moved up to a 90 so will be getting rid of the 50 soon . Now from my problem the 2004 90 if you are riding it for about an hour it locks up like it is a seized motor but will roll in neutral but after it cools down starts right back up and you could drive it no problem clutches look good anybody have any ideas what it could be ?? I know this oil in the transmission but how about with the clutches are there’s is a fill and drain plug dealer says nothing goes in there ? Thanks any help would be very much appreciated

Attached Thumbnails

90 predator 2004 locks up  ??-image.jpg