If you haven’t gone through it already, here’s the justification for this mod.
Swap the brushes out if they need it:
Then fit the plate to the starter motor body, but don’t screw the brush into the post. Hold the end of the brush between the post and the brush body in a position where it should sit nicely, and measure the distance between the center of the new screw hole position and where the edge of the end cap sits. In the below photo the brush end has moved from that position… you try holding a caliper, a starter motor, a camera and a brush end all at the same time:
In our case the original screw hole was ~14mm, and after repositioning it was ~11mm. Check yours and don’t assume. Scribe a line halfway inbetween the post and the brush. Note that we made a second mark for where the post itself was, to the right of the halfway mark. Fit the end cap and transfer the scribe mark across to it:
Measure down the inside to whatever the distance was you recorded in-line with your scribe mark. Punch a mark:
…then drill a 2.5mm hole at as shallow an angle as you can manage:
Tap it for M3, which is the thread of the original bolt:
Now you should be able to simply screw the original bolt that fits the brush end to the plate into the hole:
When re-fitting the end cap, don’t forget a new O-ring:
One of the advantages of this method is that it does not change the external appearance of the starter motor at all; though with the other methods the external bolts/rivets usually aren’t obvious once the starter motor is back in the engine.
Your starter motor should now spin over better than before!