The brushes could be held back with some light copper wire.  Then, when you insert the rotor, break the wires with needle-nose pliers.  
  One other thing rebuilders do after dressing the commutators on a lathe, is to undercut the mica between the segments.
  They'll also lacquer all the windings (both field and rotor), to prevent moisture from corroding things or shorting them out.

Mike B.
  ----- Original Message ----- 
  From: Mike S 
  To: vanagon@GERRY.VANAGON.COM 
  Sent: Friday, March 20, 2009 8:11 PM
  Subject: Re: Starter Cleanup

  At 05:54 PM 3/20/2009, John Rodgers wrote...
  >Now that my transmission is out, and the starter is easily accessible,
  >what maintenance might I do to it and associated parts to ensure it
  >continues to function trouble free well into the future.

  When I had my tranny out for repair, I took the opportunity to take the
  starter apart and clean things up. It's pretty obvious how everything
  comes apart. There was lost of dust/grime inside, I cleaned it up, and
  used synthetic grease on the moving points (but keep it away from the
  brushes). I also cleaned up the commutator with sandpaper. Use regular
  flint paper (the light colored stuff), not emery cloth, and clean any
  grit out well.

  As I recall, the only hard part was keeping the brushes pulled back
  from the commutator when putting it back together. AIR, there was some
  way to lock the brush springs so they could later be released with a
  screwdriver.

  Make sure you seal it up again to help keep water out - it was sealed
  with some kind of sticky sealant. I used Hylomar.