First, let me say I'm in the U.S. but I think that certain components on all cars have a lot of similarity. I'd state up-front, that you need to take your car back to the garage that serviced it in the beginning.
Having said all that, here's a link to what were talking about:
http://hubpages.com/h...e_brakes_can_tell_you
The diagrams at the top indicate the probable two types of brakes on your car. The left hand picture are the disc brakes installed on both front wheels and the right picture represents those intalled on both rear wheels, called drum and "shoe".
Notice, on the right picture, the part labeled "wheel cylinder". This is the part your serviceman said was leaking. Not uncommon, but on some cars the leak is at the top or bottom of the cylinder, which in many cars is screwed onto the cylinder body. It's possible the service guy tried to tighten this to stop the leaking and in doing so exacerbated the problem. I'd say that's only a possibility.
(Contd.)