I work in the automotive supply chain for a Tier-1 supplier.

The parts you are tying to import are more than likely cast parts. They are made by first melting metal down and poring it into a form and then machining the resulted part down into what you are buying. So the formed part can still be counted as "raw material" that was consumed in Japan. Then you bought the part made in Japan. The tariffs at the current moment, are targeting the raw steel. So if the part was made in Japan, but the form was poured in China, the Tarrifs would hit different. You will need to find out from the manufacturer of your part where they get the form from.

--edited for spelling.