[papajam]

In addition to the suggestions listed above, these come to mind too;

1) check that the starter mounting bolts are tight and that the special 'shouldered' bolt is in the middle hole.

2) starter relay sticking

3) and from Ripley's Believe it or Not, the cold start solenoid on the SPICA pump could be backfeeding to the starter.

To check this, the next time the starter sticks on, try disconnecting the wire that's on top of the cold start solenoid. If the starter stops, installing a relay to power the cold start solenoid should cure the problem.