Where exactly are you pumping brake fluid into your clutch slave cylinder?
A MY '83 240D with manual transmission is equipped with a brake master cylinder and a clutch master cylinder, both which share a common fluid reservoir. A cloth-braided fluid line coming off the left side of the brake fluid reservoir supplies the clutch master cylinder; a fluid leak anywhere in the clutch hydraulic circuit will lower the fluid level in the reservoir without immediately adversely affecting the brake system. Once the fluid falls below the level of the supply port, air is introduced into the clutch's master cylinder fluid supply hose.
If your clutch hydraulic system is loosing fluid, inspect the entire circuit to locate any leak(s). As you know, visualizing the clutch master cylinder will require removal of the driver's side lower dash panel. Is brake fluid leaking from the slave's bleeder screw? from the slave's push rod/rubber seal? from the clutch's master cylinder?
Bleeder valves should open and close easily, without vice grips. Are the threads on your bleeder valve rusted? Does the valve seat fully? If the valve is not seating, you'll see fluid loss. If you feel the slave is functionally intact and the slave's bleeder valve bore undamaged, then replace the bleeder valve. If the valve is rusted, the valve bore damaged or there is high mileage on the existing slave, then consider renewing it: # 001 295 68 07, up to chassis # 219674; otherwise, # 201 290 03 11. Approx. $91 from M-B. Part number for the clutch master cylinder - 001 295 44 06; approx. $99 from M-B. Don't forget to inspect the fluid supply hose originating at the master cylinder fluid reservoir; replace if necessary.
Finally, if master or slave cylinder renewal is required, ensure that the brake's master cylinder fluid reservoir seals are not fatigued and the reservoir is CLEAN, prior to filling with new DOT 4 brake fluid.
[This message has been edited by jgl1 (edited 04-05-2000).]