More switchmode power supply grief - Cisco IGS router

I have a Cisco IGS router which hasn't worked for a long time. When I was last using it several years ago, it occasionally crashed and restarted. This turned out to be due to a poor contact on a connection in the cable going from the output of the power supply to the main board. I cleaned the contact more than once but it was difficult to make it good enough to ensure reliability. When I switched it on more recently, it was completely dead, no LEDs, no fan noise, no anything. I put it in the naughty pile and it sat there for a few years before I got around to looking at it. Today I finally managed to check it out. The ceramic F4A mains input fuse beside the power switch on the back panel had blown. When I opened it up, I found a POWER-ONE MAP80-4000 power supply. The main chopper transistor labelled Q1 on the PCB is almost a dead short. It is a large plastic packaged FET mounted on a piece of aluminium which is in turn screwed to the case for heatsinking. Unfortunately, there are no markings on it so I have no idea what to replace it with :-( As Q1 is shorted across all three terminals, whatever drives it may be damaged too :-( After finding screw heads hidden under the label, I managed to extract the PCB from the case and found some corrosion underneath, possibly from leaking electrolytic capacitors :-( There are lots of data sheets available for this power supply on the web but they concentrate on the specifications for the unit and don't say anything about the components :-( There are also lots of people offering to sell power supplies like this for way more than I am interested in spending on this project :-( I could replace the power supply with a different one, however, I don't have anything to hand that will fit in the approx 5-6cm headroom :-( Anyone have any suggestions? Regards, Peter Coghlan.