I've had several 9xxx machines with sticking brakes and it's almost always a seized or corroded slave cylinder. They're easy to rebuild, but even a complete new one is only about $80. But bleeding those brakes takes some time and patience. They don't bleed easy like car brakes. Set the brake shoe adjuster between the bottom of the shoes so that you can slide the drum on easily with out it hanging up on the shoes. Make sure the reservoir is always full of fluid and leave the cap off. Open both bleed screws on the slave cylinders and let gravity pull the fluid down for a few minutes. When you start to have fluid running clear at the screws with no bubbles, close one screw. Let the other one run and watch for bubbles. When there's no bubbles for awhile and just fluid, close the screw and then repeat procedure with the other brake. Then check the feel of the brake pedals. Keep bleeding and checking this way until they feel normal again. Drive the combine forward and reverse and pump the brake pedals repeatedly. This will allow the self-adjusting mechanism to put the shoes where they need to be.