Quoting keybaud: I have traced and checked every cable from the battery to the starter motor and back again, in an effort to resolve my starting problems and I have now discovered that the problem is nothing to do with the starter motor itself or any of the wiring to and from it.
I had a low voltage at the solenoid, which seemed to cause the starter to engage and disengage erratically, although it didn't 'click'. I replaced or tested all the cables and stripped and rebuilt the starter motor, but the problem remained. This weekend I removed all the connections from the back of the ignition and tested the starter with each individual connection and I found that I only get the voltage drop when one of 2 cables are connected. Unfortunately, the wiring has been modified in the past to fit a kill switch and I'm not sure what the 2 cables actually do. They are white, but so are 2 other cables and these don't cause the voltage drop Have you done Myles' jumping trick?
Jonathan
PS: Today I am mostly happy. :-)