Many thanks. The sewing machine oil strategy seems the best course of action. I'll give it a try and see what happens. I want the machine to look good but not at the risk of damaging the finish which to be honest is in a pretty good condition. The RAF decals are more or less intact. I'll try to upload some photos.
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First photo shows staining around oil hole. Second photo shows the worst patch and third is quite difficult to see. Any ideas??