Melting back on my voltage regulator. Have you seen this before?

Hi All: Just this afternoon I noticed something that caught my eye. It appears that the gooey black stuff on the back of my NOS voltage regulator is running down the inner fender. My 1974 Duster is completely stock electrically. No modifications whatsoever. The voltage regulator was a date coded NOS unit when I bought it about four years ago. Everything runs well - that is, for a 51 year old car (headlights dim a bit when stopped at a red light, etc.). The runny part is pretty small. Have you seen this before, and is it evidence of an impending voltage regulator failure? If I need to get a new regulator, which one would you recommend? I'd like to keep it really stock looking. Ideas?

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