Did you actually strip the
threads in the post, or is it the hex head inside the grub screw that's been rounded out?
For a rounded-out head, sometimes using a SAE size Allen wrench that's just a bit bigger will give enough purchase to break it loose. My calipers are reading the supplied wrench at 1.25mm / 0.049in / 3/64ths; a 1/16th Allen might do the trick.
If the threads are stripped, and EZ-Out might do it, otherwise I think you're drilling and re-tapping the holes.. Or get a replacement deck.