Cluster Housing Refurb

So my cluster is completely dismantled and I painted the backing plates and black bezel rings. All are flat black after cleaning up and spraying a coat of rust converter. They look pretty good. Will post pics later. Question is, as I was looking at the face of my fuel gauge, it looks like something happened to it and the face has what looks like an oil stain on it. Could this be residue from a meltdown of the gauge? It has not worked correctly since I've had the car.