I've noticed that gradually over time I have to add clutch fluid more frequently. My clutch feels excellent 99% of the time and then occasionally it will feel soft. I then check the reservoir and it's empty. It's been happening more frequently as of late.

Possible leak in the lines somewhere?

 

Possible leak?

 

The lines rarely leak.

Check under the clutch pedal assembly inside the cabin to see if it is wet. If it is, your master cylinder is leaking.

Jack the car up and look at the slave cylinder on the transmission. If you see wetness there (and if you pull back the big rubber boot), then your slave cylinder is leaking.