Spongey pedal = air. Does the pedal slowly sink when you rest your foot on it? If it does, master cylinder seals. If it doesn't, go down to an accessory store and buy youself a 500mL of brake fluid (get the right type), the right sized RING spanner for your bleed nipples and a one-man bleeder (about $10 from Autobarn). Start with the wheel furthest from the master cylinder (some manuals say different but it depends on the location of the rear brake pressure equaliser). Pray that the nipples aren't rusted in and work your way around the wheels of the car. If there's any air you'll see it in the plastic tube connected to the bleeder. Check the reservoir level regularly (after half a dozen pumps or so) and keep it topped up.
I might be telling my gramma how to suck eggs, but this method works.
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