As stated by a previous poster there is not much opportunity to see manual transmission MB's in the states so excuse my unfamiliarity with the system on your car. A forum member with experience on your car or access to WIS should chime in.

Generally speaking, your bleeding process should work. Doubtful that lowered boiling point of the brake fluid is the cause. Are you sure about the quality of the brake fluid you used? Sealed container, proper DOT rating as recommended by MB (yours may be DOT 5.1, not 4) from a reputable manufacturer. Peel back the rubber protective boot on the slave and master cylinders to check if brake fluid is leaking. I would also bleed the system again. Is the slave cylinder installed with the bleed nipple pointing upwards. Is there adjustment for freeplay in the clutch pedal (short movement of the clutch pedal before it begins to depress the master cylinder piston) or slave cylinder? Good luck. Mark