Alkcnw: the eraser is called fiberglass bristle, part #14259, I believe I found it under brushes on their web site.
It is as 60103 says, it is a small brush with fiberglass bristles that can be adjusted, in the articles that I have read the contibutor stated that he spray painted one color on his project, both buildings and cars, after the first coat dried he spray painted a second coat, lets the second coat dry for a short period, enough to just set, then he distresses, with downward strokes, the project. The fiberglass eraser scratches away, with out smudging, small amounts of the second coat and lets the first coat bleed through. The person who wrote the articles goes on to say that he then adds subsequent colors and repeats the process, haveing a finished product that looks very weathered with the previous colors bleeding through. He shows photos of the work and looks very good. A very effective way of giving a weathered effect, especially on what you want to appear as old wood, be it a building or car. This method was done on styrene and very effective.
There is also a brush called the "distresser" micro mark part 82467 that ages old wooden buildings, I rarely use wood anymore, mostly styrene, but for the price may get one and try it anyway.
I have looked and called many large startionary stores and drafting places here in western Canada but for the most part no one has heard of these products, those that have state that they use to sell them long time ago but after checking supplier catalogues, are unable to locate them for me. Ron..