I restored an 1988 Trailboss 250 2x4. When I got into it the brake fluid had turned solid. I cleaned the entire break system and filled it DOT 4. They work now but they lock up 3 o 4 times a ride. They have even locked up with the ATV just sitting there. I have flushed and bled the system numerous times as recommended by my local dealership but still continue to have the problem. It is going to be very expensive to replace the system and I cant find a rebuild kit. Does anyone know what the problem is and how to fix it?