Well I guess that's a good sign (my G/B and F/D oils come out with a slight grey tinge

)
Regarding your silver flakes - from everything I've read, it's not normal and points to some sort of bearing issue. I'd pop the seal and take a look at the rivets in the bearing cage - only £20 or so for a seal. But your call of course.
The only other reference to 'silver flakes' I can find on here, is in this thread:
http://www.ukgser.com/forums/showthread.php?t=104663&highlight=silver+flakes
I have read about it on ADV too but you'd have to dig your way through some of the million page long final drive threads
M