I responded to a 2Good2Toss posting for a free sewing machine. Now I am wiser. These are the rubber coated feed dogs folks were talking about! When I went to clean out the lint, some of it came off with the solidified fluff.
Has anyone tried Plasticoat-Dip on these feed-dogs? It goes on thick, but it could be pared down to size or thinned before application.