something is definitely failing in the tranny.
some here may have missed an earlier post from you
of year make model and tranny setup. I know I did!!
A very little bit of fine silver is usually normal ( I said a VERY little).
But large flakes and syrupy is NOT normal. syrupy indicates a LOT of wear.
The magnetic stuff is most likely from bearings, shaft or gears.
The rest if not magnetic (won't stick to a magnet) is most likely
aluminum......from the case material.
Not knowing your tranny, my guess is a lock ring gave way or a bearing
gave way. The shaft has slipped sideways (maybe only a couple thousandths
of an inch or so but enough) to let shaft grind into case, or maybe bearing
is spinning in case.
I would guess you might have a new 6 speed, helical gears would cause shaft to
push side ways with the lateral load the gears naturally cause.
But if this is the case, you would normally expect harder shifting and other
abnormal noises.
Do you have receipt from dealer that did the work, this may help you with a
dealer based warranty on his work.
How much oil came out of tranny, did you save it?
edit added this: I really need reading glasses, going back and re reading your post, I see in
bottom sig line your year and model. Being 05 it ain't the new 6 speed, so it isn't the helical gears under load causing shaft shift. But I believe final drives were still helical then.
so the shaft sideways shift is still a possibility.

 

sounds like bad news for the trans. Suggest you put in HD approved fluid if you are hoping for any warranty coverage. Ken