It seems the option to build a basic Loader is not available in the assembly machines.

I can find the Fast Loader as an option, but not the basic Loader.

Just in case : I've not modified the original recipe that where defined by the developpers, the loader need an assembling machine 3 because up to 5 ingredients.

I could patch the original recipe so plate and gear would be transport belts instead and so removing 2 items to the recipe, but I don't know if that right, it would change the balance.

Definitely change this. It makes no sense that you need tier 3 assemblers to build a tier 1 loader but a tier 1 assembler to build a tier 2 loader.

+1 on this issue!