Sounds like par for the course for Roden kits.
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You've made a fine job of it, especially doing a bare metal finish over all those filled joints.
Interesting that they provide the wing spar, but not the technical direction to use it, maybe they need someone to write that page of the instructions.
Agree that a white top and day-glo orange extremities would be a quite appealing model.
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The C-124 is one of my all time favorite aircraft. I built the Anigrand C-124 a few years back, it's a pretty nice kit, zero filler required, but it is pricey compared to Roden. Still, I think I will spring for the Anigrand kit rather struggle with the Roden, the next time I need to build a C-124.