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I am not sure aluminum would be a good choice. Thermal expansion and the pressures in the box over time might lead to failures more often then with Iron. Also porosity of an aluminum casting might be a problem with the high PSI of power steering. These might be reasons but I am no expert.



Those are valid concerns, but by not making just an exact copy, and improving some design aspects with an alum version, they should be solvable IMO.
And I am not sure how the alum rack and pinions deal with these issues, since the designs differ.

Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.