I just did this a few weeks ago for my '90 240. Same style of crimped and soldered attachment.

First, I flowed fresh, clean solder into the crimped connection.

Next, I used a "solder sucker" to pull the solder out.

Then I re-flowed and resucked. And again heated the connection and rapped it on the bench to fling out the remains of the solder.

Then I was able to pull the brush out, leaving a tiny, crimped hole.

Then I reamed the hole with a tiny ice pick and several jeweler's screwdrivers 'til I had the hole opened sufficently.

Then I threaded the insulation over the new brushes' pigtails.

Then I prepared and tinned the wire ends (new brushes) and tack-soldered on a 2' long piece of fine wire to use as a "leader."

Then I threaded the spring over the pigtail.

Then I stuck the end of the "leader" through the narrow hole, from the brush side, and used it to pull the pigtail through.

Once I pulled enough through, I carefully (and gently) crimped the neck with cutters and then soldered the pigtail. I bent it over and solder about 1/8" down the outside and then cut off the excess. (You must pull enough through so that the pigtail will hold the brush properly in the holder but fully extended.)

Before installing the VR assembly, I cleaned the internal contacts with a pencil eraser as well as cleaning the contact in the alternator. I also cleaned and shined up the screw ground and mating surface on the alternator case.

So far, all works fine.
--
Don Foster (near Cape Cod, MA)