caperss

While driving my 88 560SL with 109k miles and under a fairly hard acceleration I hit a small bump in the road and my header pipe just before the converter let go. I stopped and looked and the factory weld about 4 inches before the cat (just under the passengers seat) separated as if cut. It was a perfect splice, so perfect I can slide the pieces together and you cant see the crack. It's right in the middle of the original bead of weld. Its not a big deal but out of all the cars I've owned in my life (about 40) I've never seen this happen. Has anyone else ever run into this on these cars?