My S1 is on its original starter motor, had the clicking on numerous occasions but always eventually started assuming the battery was good. Cure appears to be regular use! Cause probably due to build up on contacts exasperated by moisture.
1969 4/4 1995 plus 8 1996 Plus 4 4seater 2002 Aero S1 2013 M3W 2014 Plus 8
