Looking for some advice and easy way to make oily spots on track, I found this blog

There are numerous affordable techniques for weathering track and ballast

These are fine scale detailing since they are used for PROTO 48

On the blog, by clicking on "older entries" on the bottom right you can find a topic one about how to do realistically oily spots on track it's easy to use and the results look great

I substituted paint with wash from AK and Vallejo and homemade with heavily diluted acrylic paints but ended with excellent result fir my N scale needs

http://www.ostpubs.com