to see if it is a crack in the firewall, look where your clutch fluid resevoir is bolted to the firewall, around where that is it will more than likely have a crack or flex when the clutch pedal is being pushed. If this is the case i have a cad drawing of dimensions for a bracket to be made up to strengthen it. Also i would advise replacing the pedal box if the firewall is broken, as the crack in mine caused excess strain on the pedal box as it was being pushed in on an angle and cracked it aswell.
Johno.
Johno.