I'll post this again here as it might be lost in the build thread where we were talking about it. When printing this extension, you have to pay attention to how you print it as it impacts the structural integrity. The picture indicates you didn't print it with enough walls.
Minimum of 70% infill, 7 walls, 7 top / bottom layers.
I couldn't tell you how it was printed, as I passed the file along and got a part back. I'm not knocking those who use it, but it was cheaper and easier for me to make one out of steel. That picture is the STL file posted in this thread, so if it is insufficient someone with the appropriate skills should update it so it is sufficient for use by others.
If you have a 3D printer and know how to use it, that's probably the cheapest/easiest way. I'm one of the ones who doesn't have a printer and I've used my $7 piece of bar stock for 2 projects now and still have 80% of it left, so I'll keep recommending it to those who don't 3D print or have access to someone who will do it for them at cost.