Here is what I copied from that previous reply. Hope it helps:
Subaru CLOCK: It doesn't sound like you would want to bother repairing the clock, but if it is like the one in my Loyale, they fail due to a design weakness. Dimming the display is done with a simple resistor, which is in the circuit when the headlights are on. As this is the case for prolonged periods, the resistor is hot for many hours and eventually fails due to metal migration from the solder joint. The fix is simply to dismantle the clock and resolder the joint, a simple process and the resistor is easily spotted since the joints discolor due to the heating/migration. In my car it took about 5 years to fail, and when I sold the car last year it hadn't happened a second time after another four years.