I’d either keep it or send it to me
. I grab Mantle autographs occasionally and have two obvious fakes (most likely a parent signing for their kid), and it doesn’t bother me as it is on a vintage medium (I bought it primarily for the item it was in) and it is was it is. If you’ve got a real one already, you’ve checked that box off. Who cares whether this one is fake? For whatever it’s worth, I do share some of your views regarding the similarities between yours and the PSA one.