I tracked down a service manual for it and had a go at dismantling it. It appears the DC jack socket isn't actually soldered to the board, it's held against the board and sits on several PCB pads. Once the cover is removed the jack socket simply slides out. It'll be a piece of cake to replace, if only I could find someone willing to supply the jack! Thinking of trawling ebay looking for suitable donor phones (any nokia with the small jack socket should work).