For those thinking of picking one of these up, do note that there are two HW issues you will likely need to fix:
1) The NiCd back-up battery (2.4V, 110mAH, 2/3 AA) will be dead and possibly have leaked electrolyte onto the processor board. Two 1/3 AA or AAA NiMH batteries (connected in series) or a 5.5V 0.1 to 1 farad super capacitor can be used as a replacement. The super cap is likely to have less issue with leaking corrosive gasses/fluid in the event of a failure.
2) The power supply will need a replacement Y2 rated 22nF film capacitor (15.5mm pitch, 7mm max thickness). I would avoid using a RIFA/Kemet replacement part, seeing as how they still fail from cracking. Clearly, they don't care to fix the long standing issue with the faulty conformal coating.