If it's like the 156 and the way you describe it in the first instance - I had this a couple of months ago. I thought I'd bleed the system and lost the little pressure I had and was left with no motion in the clutch at all. Logic suggested I swapped the master cylinder, that was time consuming and quite uncomfortable to do, but it all bled with gravity and all is well. The clincher, looking back was the graunching pedal action and the black brake fluid coming out when I tried to bleed the system (fluid + seal rubber).
There are guides on the net to describe how to change this, but they don't mention it's an 8mm drill bit that makes the best pipe bung. Without this to hand during the change over you'll have a footwell full of brake fluid!!