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I'd also be checking for leaks in the system, if you are bleeding the system, and it works for a few weeks and then "feels softer" it sounds more like a leak than not completely bled.

Climb under the dash and feel around the top of the carpet, it it's damp your clutch master is leaking, also look for signs of leakage on the clutch master its-self. Next, look at that rubber clutch hose, they develop leaks at the metal crimping collar, check both ends for signs of leakage. Another hose to check is the blue hose that connects the fluid reservoir to the clutch master, they get old and leak.

Then remove the clutch slave cylinder and check that it is not leaking.

If you need to replace the blue hose, DO NOT use fuel line, you need hose specifically designed for brake fluid. Brake fluid will cause fuel line to deteriorate from the inside out, and fail at the most inopportune time (not to mention contaminating your system).

Seriously, consider the power bleeder, you will make your job much easier when it comes time to flush and install new fluid in your braking and clutch system...this should be done every 2 years.