fix it or get a new system?

I have a 02 Renault grand space and My clutch has completely gone flat to the floor. I was told I need a complete new hydraulic system and it would cost me about £800 give or take a few pence. Despite this I have dismantled my dashboard and removed the master cylinder along with the clutch pedal. I had fluid leaking down the push rod and am hoping that the problem is a seal in the master cylinder that can be fixed simply by replacing it. Am I on the right track here because I can't justify paying that much money for new parts that I don't need or would it be wise to replace the lot.