Haven't used them but a reasonable way to do it.
http://www.blackstone-labs.com/free-test-kits.php

You're probably correct about the particle ball on your magnet, but a much more
telling sign/symptom of the condition of your tranny is the color of the oil. When
there is an aluminum "sheen" to the dark color of the lube, that indicates that the
case is breaking down, which is symptomatic of high heat cycles, and vibrations
at the bearing points, not so much the gears themselves.

bob
On Aug 22, 2013, at 1:13 PM, Mark McCulley <markmcculley@GMAIL.COM> wrote:

I'm changing transmission oil after an extended period of neglect--hasn't
been changed since the transmission was rebuilt almost 70K miles ago. Is
there any value to having the oil analyzed? If so where would I send it for
analysis? There are some filings on the magnetic drain plug, a ball
slightly larger than a pea I'd say. I presume this is fairly normal? I'm
not experiencing any issues with the transmission, just trying to catch up
with long deferred maintenance.

-Mark
'87 Syncro Westfalia