I have a 88 mercedes 260e and my rear brakes aren’t working. for a while I’ve been driving the car and the ABS light flashes sometimes and the brakes worked fine but they sqeaked really bad when the brakes were warm. my uncle said that there is something wrong with the caliper so he checked them out. He took it apart and notice the rust on the piston. so he sanded the piston and the piston bore and kind of repaired it.He said he did this all the time when he was a teenager in his country. After we got done with the job we tried to bleed the brakes but nothing but air comes out. we were bleeding them for more than 2 hours trying to figure what was wrong. we bleed each one by one, rear right to rear left to front right to front left. we tried bleeding with the engine on and the engine off. So we are stumped! now the car drives with only the front brakes. I need serious help. what could be wrong?