A couple of things to consider
Do you care about matching numbers and those sorts of details? The originals are dated
So if that is important your likely rebuilding this one. If not it might be trading or sales material to another owner looking for a certain date
Is yours in good shape other than the rubber? No hammer helper dents, rust pitting or damage ....? If so you might choose the repo
Not aware of any rubber gasket on an original gas cap I can remember