Mountfield petrol mower that has stood for 5 years?

Ok, a friend has just asked me to look at his mower, the sump is full of petrol, on turn over the fuel pours out the exhaust and the maching sounds like its "crunching" at the crank. The machine has been lying unused for 5 years and the origonal petrol is now varnish and has gummed everything up. Yesterday he put fresh petrol in the tank and tried to start it, nothig happened, of course:-). My problem is this, what damage has been done to the crank, bore, seal etc and, is it worth while trying to repair the machine as a new one is only £159 at B&Q