I have a MOW jet pack, and on one side where you drill the hole where the thruster mounts was way thinner than the other. Mine looked like it was starting to crack when I drilled it, so I mixed a little bondo and spread it on the inside all over the thin spot. This was no biggie, as this is a kit and a little prep work like this is normal. I assume this what happened to yours. If yours is just cracked, you could try the same or even mix a little fiberglass resin and pour inside over the cracked area. If you actually broke a piece out. I would superglue or tape the piece back in place and than mix fiberglass resin and pour/brush on the inside. This should thicken up and strengthen up any weak spots. Let us know if you get it fixed and what worked for you. Good luck.