A904 debris in pan

Two summers ago, the A904 transmission in my 63 Valiant stopped working while driving. After about 15 min, it started working again and I was able to drive it home. I dropped the pan and discovered that the mesh screen (this is original and has a metal mesh screen and an external filter in the trans fluid cooling line) was plugged with a fine grayish-blackish silt. Very fine particles that were sticking together in the screen. Cleaned the screen and it worked fine.
I did not think it was unusual, as it looked like the pan had never been off of the transmission before.

This past summer, the same thing happened. The only difference was that, this time the grayish/blackish debris was larger in size, and not simply an emulsion of fine particles.

Is this a common problem with a known solution?

Should I just have it rebuilt or replaced?

Thank you!