I've always suspected that it was an economic decision by Mitsubishi to deal with the problem as a warranty issue.
Do you spend a million dollars to fix/replace a manufacturing jig in a factory where the car may not be made much longer...or do you just keep cranking out cars and fix the ones where the owners actually complain? These cars are sold all over the world. I'm sure in many non-US markets the roads are terrible and wheel alignment is a luxury.
Even in the US, most Mirage owners are uninformed/complacent about the issue. How many Mirages sold in the US in the last 4 years probably need a new rear axle? Maybe 1,000 or more? How many new rear axles have been installed in the US under warranty? I don't know...I bet it's not more than 100. If you're a bean-counter, it's a no-brainer decision. It's cheaper just to fix the few that pop up before the warranty runs out.
The other thing they could do is check/correct the alignment as part of the pre-delivery process in certain markets (like the US). Apparently that's too expensive as well. I know I won't buy another Mirage (new or used) without a 4 wheel alignment sheet in my hand.
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View my fuel log 2015 Mirage ES 1.2 manual: 52.2 mpg (US) ... 22.2 km/L ... 4.5 L/100 km ... 62.6 mpg (Imp)