Ulli, you got lucky if the defective heater hose did not rupture while driving and scald you or your passenger's legs with live steam, as has happened to several U,S Pantera owners! When owners replace heater hoses, they invariably forget to change the little ones under the dash!
There were two versions of the heater valve- '71-72 and '72L and up. The later valve uses a metal arm running in an inclined slot to raise and lower the shaft and thus open and close the hot water flow. What leaks is a tiny o-ring inside the valve, which is available in Viton (I think) from McMasters-Carr, according to several articles in the POCA Newsletter over the decades.
The two valves are equally ineffective at regulating hot water thru the heater core. Due to mismatched leverages between the valves and the levers on the console, you can either have the heater work well but leak hot water when 'shut off' which degrades the A/C, or you can adjust the controls to fully shut off hot water and degrade the operation of the heater and defrosters. There is no easy fix for both conditions beyond replacement with a completely different type of valve, or maybe use Maserati BiTurbo parts as one owner did. Good luck-