02 Honda CR Rear Brake Problems

My friend with his '02 CR 250 has had this happen to him like 8 times now. There really isn't any cheap way to fix it other than constant bleeding motual 600 brake fluid won't fix it just lessens the chance of it going out alittle bit. I was wondering if getting the master cylinder/resovior the '03 Kx's come with would fix it maybe. It holds the same amount of fluid as the older design and the rubber seal is smaller like the older designs I won't be surprized to seem that design become more common. Thicker after market brake pads help some also.