Checking the fluid level is the first thing, any major discolouring can suggest heat transfer been a possible cause, air is the most likely issue getting trapped at the end of the master cylinder, bleeding should be done with the help of an assistant, a final check is to get an assistant to watch the master cylinder for bubbles whilst the you depress the clutch several times in quick succession, any bubbles mean the master cylinder drawing in air at the rear seal.
The flex pipe replacement as mentioned above is also recommended at some time even if you sort it now by bleeding the system.
Jeff TT