1987 Yamaha Champ - Oil drain cracked in half!!

I (original owner) have a 1987 Yamaha moto 4 champ 100. I went to change the oil a few weeks back and the oil drain plug cracked in half! I attempted to fix it using JB Weld and tapping the thread but it ended up breaking off again when screwing in the bolt.

Anyone have suggestions??*(Pictures attached)

Thanks in advance!