get an electric from repco (about $105 IIRC), pull the arm out of the latest broken one and use the old pump to fill the hole... We done that on a mates chevette and if ya hide the electric and run some dummy hoses to the mechanical one, no prick will even know... took 20 mins.
edit: and if ya dummy the pump and the diaphragm is fucked, pull it out and replace it with some gasket paper/rubber/goo/whatever ya wanna use