That silver is all the metal shaving from the chewed gears, smae happens in shocks, nothing to worry about. I will be re-building my diff's in my ST-R this weekend and will, i assume, find similar issues as you. Have 2 gallons in mine so it lasted longer than most but not as long as it should

I will probobly run 10k front 15k 3k rear, I ran with stock as well, was prtty good for me so dont plan a drastic change, so yer setup should be good

stav