Rear end leak after TSB

I had the TSB done on my rear end (rim shot....just for you chicken!) this last summer and it's leaking again. I have a spot on the garage floor that is 4"x4" and its all over the undercarraige. Should I be concerned? I've noticed the rear end has felt a little odd lately...almost like it's shifting front to back when I accelerate. The fluid is coming out of the vent tube. In it's defense, I drove on freeway, and put it in the garage. It's been very cold here. Should I take it in and pay them $100 to diag?