Let's stick to 2d6, I think.
Going up to Garg works, too.
It looks pretty good, but we need to do something about the magic aura DC; it's really wimpy for the HD. Switch to Su? Boost Cha? Make the DC be based on a weird stat?
I'd say make it Su and drop the CL bit. A couple other revisions:
False Magic Aura (Sp or Su): Once per day, a metal mimic can give itself or a part of itself a false magical aura, as per the magic aura spell (Will save DC 12 or 16). The aura lasts for 24 hours, or the metal mimic can cancel its magic aura as a free action. The save DC is Charisma-based.
How's that?
Crush is probably ok (or does it need more damage?) -- and why isn't this constrict?
Is mimic shape finished?
We can reduce the duration if you want; the Sp version had 1 day/CL duration, so it's already reduced a bit.
Let's go to half-standard treasure across the board.
The AC is a little soft but not ridiculous. It's ok if you want to leave it or if you want to bump it a point or two.