Sorry for the ambiguity of my original post -- new to this site. Yes, I'm referring to hydraulic fluid for the clutch. Again, I apologize for not using the most appropriate lingo.
This condition has been going on for a while. It use to be that a full reservoir would last a month, and I just kept an eye on it. But nowadays, it'll run dry in less than a week if I don't stay on top of it.
When the reservoir has fluid, the tranny operates perfectly. But if I ever run it dry, the transmission will get increasingly difficult to shift to the point where you can't shift any longer, and there is no longer resistance in the clutch pedal. Then simply adding fluid back into the reservoir and pumping the clutch pedal several times, and everything is fine again.
So if fluid is indeed leaking behind the firewall, the master cylinder is faulty and replacing it will solve this problem?
Thanks again for the comments and insight. I'm a relative novice here.