Slave cylinder is on the front of the gearbox and its a piece of you know what to change :-D If its leakin you will see that the front of the gear box bell housing will be covered in fluid and stained.
Changin is easy, only a couple of bolts hold it in place plus a clutch pipe and pivot into the gearbox. Once changed its just a case of bleeding the system through the nipple on the slave cylinder and job done
If memory serves correct i seem to recall the being about 40 to 50 quid from nissan.
If fluid isnt leaking from the slave then you need to trace the pipework back to the master cylinder and look for leaks around there. As Paz said, if the Master is gone then your clutch pedal will be covered. This is not a nice job to do :sad: If youre half handy with the spanners it will take a few hours to do and there isnt alot of room to work in :doh:
Start with the slave and work back anyway.
J.