Transmission Question - How concerned should I be?

[CleaningTheGarage]

Pulled the shift tower and thoroughly examined all the gears. No broken teeth or other damage consistent with the shard I found. A little burring on the edge of a few teeth, but doesn't appear to be enough to account for all the "glitter" in the cap. To me it looks great, but I'm admittedly ignorant.

Briefly considered it might have come from the "cup" that holds the spring in the shift tower, but the shard material is too hard to be that.

My new theory is that the cap wasn't cleaned out during a rebuild, or got swapped with a cap from a trashed transmission last time it was out.

Unless someone has something else to check/try, or input based on the pic attached of the open box, I'm going to flush it, close it, fill it, see how it runs and go from there.

Thanks a million for all the input!