It would have to be REALLY new for you to not be able to see the difference. It darkens noticibly in just a few months.
Also, don't sweat it too much.
If a small amount of the old stuff remained, the world would not end. The worst of it is in the caliper itself (the lowest point in the line). That is where the water and sediment settles to over time.
1986 300E 5-Speed 240k mi.