If it was mine, I would restore the seat that you already have, with a red foam and cover from Yamiya. Cheaper and more correct - from memory Yamiya's new seats have a seat base which strictly is only correct for the first thousand or so sandcasts (the base has a different arrangement of holes as compared to your base). Yamiya's are great seats, but you do appear to have the correct seat base to start with.
Just my view - Chris R.
Hello Chris,
... too late. I orderred it today and paid by paypal....
So I will keep the old seat just for patina´s sake.