Where is the fluid coming from?
If you pushed the piston back, that would push fluid back into the master cylinder (on the bulkhead above the gearbox) which, if you had the lid off the reservoir, could overflow the reservoir and run down the outside of the master cylinder and follow the metal brake line so that it dripped inside the wheel arch.
Make sure it's a leak and not a "spill".
If it's a split pipe somehow (though I'm not sure why it didn't leak when you pressed the brake pedal, rather than just pushing back the piston, which is a much less powerful force) then you need a new pipe.
New pipes are impossible to get hold of, so you will need to remove the old one and bring it somewhere to get made.
The old one will also be impossible to separate from the flexible hose (despite however much penetrating oil you use) since as you turn the nut, the metal hose will twist and collapse - there's no way back - so you will need a new flexi' hose too.
If the flexi-hose is split, then "as above" for the very same reasons.
The good news is that even if you fit a new pipe and flexi' hose, the brakes are dead simple to bleed (no ABS) or "slightly tedious" (ABS). Use a pressure bleeder to avoid pumping the pedal too much, since the master cylinder isn't used to a long brake pedal travel and occasionally the seals go walkabout and there's no easy way to fix it. If you have to pump the pedal, then use short strokes or slow strokes so that the master cylinder seals don't twist.
Ralf S.