I'm going to wait out on another subframe in better shape and reinforce it, I didn't realize how much crap that area of the subframe is... apparently it is a common problem for 2 key areas on the rear subframe 1.) right where the front diff mounting bolts and subframe meet 2.) above the diff where it connects to the driveshaft. everyone should go under the rear of their car if not already done so and check these areas of your subframe. I suspect that age and the more torque the diff puts more stress that causes these cracks.
I found tons of info and pictures in detail about this particular problem
http://www.supraforums.com.au/forum/...p?t-43162.html