I’ve just installed the front differential in my Truggy (once more: terrific work Daniel Norée !), and I have a question/suggestion. Why use a M3x6 countersunk screw to assemble the top to the bottom of the housing? From looking at the step file it’s the only place where such a screw is used, and I didn’t buy any (I just fixed my copy of the BOM at https://github.com/rdolbeau/OpenRC/blob/master/Truggy/BOM.md, and expanded the build instructions in the same repository).
I’m not a mechanical engineer, but it would make sense to me to make a thicker upper part and/or to add a matching hole in the horizontal bar so that the design would use a longer screw of a type already in use such as an M3x12. Shorter BOM, less expensive build? (I get my screws from conrad in pack of 100 
Just a thought