I think you should be fine with either one.
I agree with MiniHomesteader, you'd be ok using either needle seat including your old one if it's in good shape. I'd lean toward using the new one though vs using an old one as long as you have it apart.I am rebuilding my Carter model N. The new needle seat is different from the old. It has two holes in the sides near the base.
Which should I use, the original or the new one?
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Thanks for your input.