A lot of the Forester clocks seem to quit or go intermittant. Mine was a cracked solder joint. To fix, you need a fine tip soldering iron and half an hour. Maybe a resistor, but mine just needed resoldering.
Pry out the clock at the retaining tabs at the top, and unplug the connector. Take it to a table before you take it apart or you'll lose the tiny buttons... Remove the circuit board and find the resistor with "510" marked on top. If it's cracked in half, you'll have to change it. But probably you can just resolder one end. If you need a new one, it's 51 Ohms, 2 Watts. Find it in the DigiKey catalog...
Reassemble in reverse order of disassembly.