Hub Drain Plug / Acceptable amount of contaminants?

[Switch3287]

I have done a pretty thorough rebuild of all the hubs on my 1078 (twice actually). The first time I flushed out the fluid took it down to the axel nut then re-shimmed everything. Drove it maybe 10-15 miles and I had a pretty heavy buildup of what almost looked like molly paste on the plug. Next rebuild around I took all the hubs off clean and resealed them too ( ams oil grease and oil ) but after another 10 miles I still see metal paste on the plugs again! When I first got the truck there were some issues in the hubs but everything has been cleaned and damaged parts were replaced as needed. is this ok or should the plugs be pretty clean after a fluid flush?

 

[Third From Texas]

Seems like old residual gunk? I mean, I'd think that ten miles isn't enough to wear anything enough that it creates a reside.

Is this present on both the front (independent) hubs as well as the rear (shared with dif) hubs?

I'd do another flush after awhile to see if it's simply residual.