1938 Woodie - closing gap in wood frame

[Jacques1960]

The wooden frame and panel insert gaps are all tight, with the notable exception of the right rear middle horizontal frame member, which has a 1/4” gap relative to the tailgate frame. Before I begin any disassembly, is there an internal means of closing this gap mechanically (tightening a screw or bolt) or is a longer, replacement wood member called for ? Photos to follow .Thank you.