I looked at the ebay link, downloaded the picture and blew it up. There is a C9 part number on the back, and a rectangle that I can't read well except to say it has "letters" in it that "sort of", "may be" FOMOCO. If it's supposed to be FOMOCO in a rectangle, the part number should be be a C4 or C5. A C9 would be FOMOCO in an oval.
As it stands now, I would say it's aftermarket.
Jim