Do you fish around for the locator pin every time you insert an R8 into the spindle? Use your hand held electric drill to cut a small, shallow hole in the perimeter of the spindle right over the slot. It could be 0.1” in diameter and 0.05” deep. Fill it with red nail polish and then wipe level. Alternately, you can grind a shallow groove with a Dremel and fill with nail polish.
If you want to be extra fancy, grind tilted lines +/- 90° from the slot with the low end closest to the slot. They will tell you which way to turn the spindle to get to the locating pin.