The thing about T-bars, I'm sure all of you know, is that they take an insane amount of abuse, by design. They are hanging down there, totally exposed, for the life of the car. They will all have rock dings, impacts, dents, etc. I know have I have beat the living snot out of mine taking them off and putting them back on multiple times. As-manufactured they already have a pretty rough surface, so I don't think the little stress raisers from over-the-road abuse are going to have much effect. In a nut shell, they have a very high damage tolerance. I think it's pretty rare to even see broken bars in 40+ year old iron. They just don't usually break. At least that has been my impression having been in the hobby for 20+ years.

But when they do break, in only 1 YEAR after purchase, all sorts of alarms should go off in your head. I think we all agree that there are some fatigue features. But usually 70-80% of a fatigue life is consumed in initiating a tiny crack. 20-30% is consumed in growing/propagating the fatigue crack to final rupture. Maybe this bar started cracking 8 months after installation? What lowered the threshold to fatigue initiation?

And that long flat planar feature? What stress state would cause THAT?

I say infant mortality...