Chris, I have the fork disassembled in front of me. The valve is enclosed inside the damper tube. The seat of the valve appears to be swaged to the damper tube. At the other end of the damper tube the cap is also swaged to the tube. Circular swages, damper tube deformed around the seat of the valve, no divots.
It appears the '03 43mm Showa is unlike previous 43mm Showas. It seems like it could also have been built with a damper tube threaded at both ends with threads in the valve seat and cap but instead the ends are swaged. It seems especially bizzarre because the cap and the valve seat have flats for screwing.
If anybody has a workaround, please send me a line. These forks appear to have non-replaceable valves, like the old Marzowhachamacallit.