Wierd Clutch problem

1995 MITSUBISHI 3000GT BASE, Millage=158,000. Hi: I'm having a weird problem with my clutch. One day, I started the car with the clutch engaged and I tried to put reverse. But it wouldnt engage. Then I tried to put 3rd gear, just to see if it was the transmission. But it didnt engage too. I disengaged the clutch and engaged it again, and I was able to shift normally. After some weeks, I was in a red light, and I felt the clutch pedal starting to lose pressure, until it went dead. I pumped the pedal several times, and it came up again with normal pressure, but after driving a few block the pedal went down again and lose all pressure, and I drifted off to my parking slot. I tried pumping the clutch again, but this time it wouldnt get pressure back. I opened the hood and saw that the fluid level was not full, like it had always been, so.I thought that something was leaking, after cheking the lines, I ended up with no leaking, and I also checked the slave cylinder, but it traveled well when the pedal was pressed. The same day, just 4 hours later, I started the car and the pedal had pressure again. Also, I dont know how, but the fluid level was back to the normal "FULL" position. Now the clutch is working normal, but I have to engage the clutch all the way to shift normally. Im afraid that something will go wrong on the next days and I dont want to brake something that is working well. Some mechanics told me it was the master cylider, or that the clutch was not traveling all the way that it should, I dont know what to do, please answer me guys, thank you