go back to the motor and look at the armature bars real close.
that glowing you saw was the residue or possibly a chunk of copper off one of the bars shorting against the next bar.
There is one critical step alot of guys forget to do or just don't know to do and that is to clean out the gaps if your doing alot of resurfacing and then following up with a polishing stone.
So go in and check between each bar and make sure there are no bridges of copper built up. You can take a tool they make for cleaning the gaps and truing up the edges of the bars to make a clean gap.

I stoned the commentators on motors for years , with hit and miss results. yesterday I stoned one on a RD5200 Crown. The way I do it is to jack up the truck , pull one set of the brushes out , start motor running and stone the commentator.
Then all of a sudden it stopped and I saw a red glow in the motor just past the brush holder. I shut it off real quick , but now when I start it up it says "Please stand by" for about 20 seconds and the codes out to a 329 and 321.
Following the book I checked the modules 2 and 3 and they checked good.
I blew the motor out real good to, still no start.

Thanks Swoop. Have ordered new motor.

you can try to rebuild the motor but 9 times out of 10 the armature is generally trashed and would also have to be replaced, the expense of this is almost the cost of a new motor.

You can try to resurface the armature commentator but you will find after a short period of time the 'clicking' will return even under normal operation and cause drive error codes relating to open drive circuits because the brushes will start jumping off the bars again.

If you take a closer look at these sections that are raised you will find they correspond to where the brushes are related to their positions around the brush housing. This 'raised com bar' scenario is caused by stalling the motor usually. The com bars get hot, the resin that holds them together gets soft, the bars raise up from the centrifugal force being applied when the armature is turning. Once this happens there is no 'fix' for this, it will continue to happen until the com bars just short out or come apart.

using a seating brush or resurfacing stone or even rebuilding the motor and cutting the armature com bar surface down may temporarily fix this problem but the 'real fix' is to just replace the armature or complete motor.

Thanks Alanmitsi. Will rerbuild.

Commutator has a high segment could try a skim but if its let go will need a new one