I've seen that in a few Singers. It turns into something like wax, and freezes up the machine. Sometimes we have to break it off in chunks, with a small screwdriver. I imagine that the grease is along the upper shaft and in the gears, as well. The machine probably turns very slowly, if at all. And I'll bet you can't get it to make a zig-zag stitch. It's hard to remove when it hardens.