I just recently replaced both cylinders on my sprinter...if you want to do it yourself, find out which one is leaking the slave or the master or both (i would replace both anyway). The master is the one your fluid resivour is directly connected to. The slave will be down lower and connected to the master with a metal line.
Remove cylinder(s), this can be a real pain in the ass, moreso if you have a small japanese car.
Ring around local brake and clutch places for replacement cylinder(s) for your model.
Get replacements (take your old ones with you to make sure you get the right bits)
Install new ones
Fill and bleed system.
Done.
It cost $82.50 for new slave and master cylinders for my car, it's worth ringing around too, one place wanted to charge me almost that much for just the master cylinder.