noticed a gearbox oil leak when i forst got this impreza, and clutch was slipping real bad was hard to pull away in first, (lots of juddering, and biting right at top of pedal)

1 month on, noticed the gear oil level has dropped from full to the empty line, and is leaking quite bad, have clear gear oil on the concrete under the car right now.

Where are the possible places it could be leaking?

ive got some ramps you drive up outside, will put her up on them tomorrow, Whats the best way to find the leak?
clean of the whole area and see where its coming from, or clean up take it for a short spin then see?

Are there any common leaks of gearbox oil?