Slip joints are utter garbage, we had the same problem with the clamp always letting loose on the Solo Performance exhaust on the Solstice. Our solution was to buy V clamps and weld em on. The bonus here is we had 2 rear sections in case we had issues with meeting sound, so they each had a mating collar in case we ever had the need to switch, it was super easy.
http://www.jegs.com/p/JEGS-Performan...98388/10002/-1
Buy a pair of bands, a clamp, and you've got an interim solution for your track days, it could be a long term fix, but that sucker looks pretty mangled...
But yea... I read their response as "Agency Power does not design their product for track use"... so if you plan to track the car, probably should look elsewhere to those companies who do design for track use.