HELP: Interested in what saturntech9 might think.

HELP: Interested in what saturntech9 might think or any other Guru (clutch hydraulics). Helped step daughter by this Saturn 2000 LS (listed as LS not SL) 4 door, 2.2 lit, 5 speed. Car operated great for 1st 2 days. Clutch started to fade the more driven. Then Just off the floor. Pump clutch 8-10 times, pressure back. Have done 2 full power bleeds my self. Still returns back to no pressure without pumping. Took vehicle to supposed saturn expert (twice) power bled, reverse bled. No air in system. Drove 15 miles let sit over night. Back to pedal on floor. There is no leaking at master. No fluid coming from bottom of tranny and no fluid loss in reservoir. I've been over this for weeks, no one at chevy knows, etc. I no that system usually installed complete/sealed from factory and non-serviceable even with bleeder on slave junction of bell hosusing. With slave inside of transaxle, complete replace of clutch slave is spendy at shop to pull tranny all on $900 car. Question (1): Is it simply possible that fluid is blowing bi-directionaly in the master. Allowing for temporary hydraulic pressure then fading back at rest. And if even just the master replaced and bled might remedy. Question (2): directly between the master at firewall and the hard line to the slave is an unknown 1.5" metallic yoyo shaped valve of sorts. What is that and can that be the offender. Since parts and info at Chevy have been near impossible, might the replacement from a salvage yard of master, yoyyo, hard line and bleeder attachment solve this without pulling the tranny. Any help would make this new daughters car drive-able - Thanx upfront