Started to develop a steering wheel / seat shake at idle / stopped when in gear - ordered a set of replacement motor mounts and a transmission mount as everything that I've read suggested these were the symptoms. My mechanic called today and told me that it wasn't safe to replace the engine mounts as the frame was rusted through. Fortunately he was able to find a junked subframe and will have mine replaced. Still, having a 12 car in the Northeast will do a number on the frame - please check yours as my car wasn't safe to drive on it.

 

Interesting. Aren't these made of aluminum?

 

The part rusted through / replaced was 544B2-EG300 - lower subframe crossbody. Pretty sure it's made of steel. My sense is that the years of road salt did it - in addition, my neighborhood was flooded in 2012 by hurricane Sandy and I and my family barely made it out of our driveway before it was flooded by salt water (the underbody of the car was most likely exposed to salt water). The replacement of motor mounts & transmission mount made a world of difference - car feels like the day I bought it, tight/solid with no vibrations of any kind.