shovel -
I agree. As long as the car's emissions are legal for your state, then I think you are doing your part.
Part of the irony of "my old car" is that I've learned a lot about keeping my specific drivetrain alive. If I lost my car tomorrow, I would want to give another used version of the same car a chance because I know how to take care of it. I have a "vested" interest in my drivetrain because it's what I know.
Your equation makes my car 25% recycled,
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CarloSW2