The high flow coolant pump motors on both our SL10s would not start because the flange moved by the centrifugal weights on the starter switch wore and would no longer close the switch. This flange is retained on the motor shaft by a circlip and when the motor stops the flange is up against the circlip. The quick repair was to machine a counterbore about 0.03" deep so the flange could move out this much further and compensate for the wear.
One motor failed at around 750,000 starts and the other at around 330,000 starts.
I had this same problem and went to fix it (don't remember the fix, probably similar) but the thing flew apart after a few more starts!
Of course mine was do to install issues not fix issues. Now the motor is sitting around until I get time to take it to a motor re-winder.
If it wasn't for bad luck I would have no luck at all!
"If you don't stand for something, chances are, you'll fall for anything!"