After 10 years of hanging on the ceiling it's plenty dirty!

But seriously, at the time I was building this I was aware that many of the original EIII's had all sorts of assorted dirt and oil stains but just didn't have any idea how to simulate that on a model. BTW, I'll be bringing this model back with me to Japan and hope to get it flying again soon. And if that project goes well, I might think about building a set of scale, warping wings, since when I built the original model, I had that in mind and made allowances for it.
Note: In comparing the model with the 1/4 scale Proctor plans, I discovered that the BUSA eindecker isn't really 1/6 scale (which isn't really surprising since it's not really scale anyway). The wingspan is 60" while a 1/6 scale EIII would be 66 inches. So I guess that makes it more like 1/7 "scale" or thereabouts...which explains why the 1/6 scale WB Spandau didn't quite fit where it was supposed to fit.