Did my second front and rear diff oil change today. The first one was at break-in, this is 1 year/ 400 miles later. The oil (conventional 80w90 gl-5) came out looking brand new in color. However, quite a good amount of debris stuck to the drain plugs both front and rear. Obviously metallic but looked more like black dust/dirt than metal shavings or chunks. I don't remember seeing this after the break-in oil change but the bike hardly had any miles on it then. Does this look normal or should I be concerned?