MGBsuperb

Hello Can anyone help with advice? 2015 ŠKODA Superb estate, tdi 6 speed manual, now done 125000 trouble fee miles. For a few months the clutch pedal has felt soft, this is improved for a few moments by pumping the pedal. The clutch bite point can vary, is often low in the pedal stroke. There is no hydraulic fluid loss? The car has always been drivable despite all this. The clutch is original and does not slip. Gear shift is fine but sometimes tricky unless the pedal is pumped, maybe once a week. All this suggests to me there is air in the clutch hydraulics. The local dealer bled the clutch last week, but it has made no difference. Is it worth bleeding the clutch again? I have read elsewhere here about the concentric slave cylinder, is it possible for it to fail without leaking? Thank you