Pumping the clutch to regain firmness points me to rebuilding lost pressure.
Two possibilities I can think of:
- air in the hydraulic clutch system, either it was there or has crept in from worn seals in master/slave cylinders. I'll put my bet on the slave cylinder.
- A bad pressure plate - I wouldn't go down that route just yet.
I'd take the slave cylinder off, open it up, inspect the inner walls - if there are any pits or rust then you'd need to replace the slave cylinder with a new unit. Unless its inside the bell housing, a 10min procedure imo.