Regarless...it is contamination. Probably due to wear. If it has never been changed, it may be a combination of wear and moisture. After changing, it may be best to check it every few months to see if it changes again. If so, a seal of mechanical part may be failing.
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well-preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming: Wow - what a ride!"