This problem was never resolved in my now dead 740.
Just pull the weather boot off the heavy terminal at the starter.
With your key on (KPII) take a husky screwdriver and touch the heavy terminal and slide the screwdriver to the small solenoid lug.
My car would start right up and sometimes behave for months afterwards.
I wonder if there's some crappy connection at the solenoid lug
maybe some riveted lug that gets corroded and/or loose.

The problem is in the solenoid operation.

Be sure that the push on spade lug is tight.

There's one last thing, there's two lugs at the starter solenoid for the
single solenoid wire. One on top and one on the bottom. You might try
switching the little wire to the other lug, see if it works better.

Good luck, Bill