Y-Axis is fiddly

I am assembling a Prusa i3 Mk3 3D printer kit. The assembly manual breaks the process into sections and the first one is Y Axis assembly. I pulled together the parts labelled for this section, the photo shows most of them, but there's some steel rods and a motor that's not shown.

The first part puts the basic frame together. It seemed fairly straightforward until the check that the frame sits level. I needed to put the frame on a flat surface and check that all four corners sit on the surface with no wobble. I had wobble. The manual suggests loosening the bolts and pressing down on the frame while retightening the bolts. That didn't help.

One thing that the manual suggests is that Prusa can help, so I looked at the comments section of the online manual. Lots of other people seem to have the same problem and always the front right and rear left corners wobble. This must be a design or manufacture issue, but there were suggestions to fix it. I swapped the positions of two extruded parts and loaded about 8 kilos of load to flatten the frame before tightening the bolts, being careful to do them up equally. That seemed to work and the wobble is now less than the thickness of a sheet of paper. Prusa say that's fine.

The rest of the build of the Y axis section was just as the manual described, so now I have a frame to build the rest of the printer on.