I'm not surprised that the JB Weld repair came loose. I'd order a new pan, but if you're feeling overly thrifty and since the threads are OK another approach for a shade tree repair might be to get a thick "fender washer" sized for the drain plug, snug it in place with the plug and then seal weld around the outside of the washer to the pan, being sure you cleaned all of the old paint, JB weld, etc off for a good, clean weld with no pores. A new pan's gonna remove all doubt, and will definitely look better until you bottom out on the speed bump again.....