Same symptoms here.
Cause: engine lid seal not sealing + stupid sound pad in engine compartment = hole rusted through firewall just above the cable.
Here is a pic of mine.
http://members.rennlist.com/a914lover/page5-4.htm
------------------
CWP/VIR
72 914 L20E in rusto.
73 914 L20E 2.0L in resto.
http://members.rennlist.com/a914lover