my 4520 ran fine for the last 3 years and now warranty is up (4 months ago) now its time for brush hogging. wouldn't you know when the brush hog is raised pto works fine. then i lower the brushhog and start moving my pto stops.... why is that. the dealer wants 80 bucks an hour to trouble shoot. i pulled my cluch on the brush hog no problems there so it has to be my tractor. any ideas or waste 80 bucks