A design flaw, perhaps.
Anyway, I have merged the inner half of the pipe joints with the Manx roll bar and uploaded the stl file to the Beach Buggy Body Set on the Google drive.

When I was working on it today I asked myself the same question...it was so long ago I don't really remember doing any of it or how it was done...I do remember they are from a Tamiya...I am gonna go back thru the thread and try to find it