a couple weeks ago the clutch on my 1997 nissan pickup xe 4x4 started to act strange...it would not fully engage so it was very difficult to shift...i replaced the slave and master cylinderd and have spent countless hours using different methods to bleed the system...there is nothing but fluid in the lines and cylinders but still the clutch wont fully engage...i can see that the slave cylinder is only pushing the pressure plate out about half way...i am dumbfounded...also there is a "mystery part" located under the fuel filter mounted to the firewall about halfway in between the master and slave cylinders with a bleeder on it...i cant break the bleeder screw free...i used an oil squirt can to "reverse bleed" the line form the slave bleeder up through the master cylinder reservoir...STILL WONT FULLY ENGAGE! STILL HARD TO SHIFT!! a friend suggested a bad throw-out bearing?? is this a possibility?? thinking about replacing the entire clutch but wan to be sure of my problem! has anyone else experienced this problem?? any suggestions greatly appreciated!!!