In the past days I tried to find a solution for the missing flute. Sling Aircraft offered new parts but these will take some time to fabricate and ship and will require removing quite some rivets.
I started with modeling the flute with forming tools by using the same dimensions as the existing flutes created by Sling Aircraft:
Next I CNC machined the forming tools from mild steel and welded them together, to apply clamping-pressure I used 4 M12 bolts:
After some tests on scrap aluminium it was time to create the flute:
Time for some new epoxy primer:
Now all holes align with only minor match drilling, so the side rail can be riveted in place when the primer is cured.