Mercedes Benz 300e goes out.

I have a Mercedes Benz 300E Model 1989, on many occasions, when brake or down the car goes out, no mechanic has found the fault, the only one was to graduate the controls to be more accelerated, thus and lasting for a year, but it is very difficult because it is automatic and you have to be braking a lot, wearing the brake pads.
Much would appreciate his wise advice on the matter.