Heng Longs use PVC plastic. Use that plastic plumbing glue and glue a piece of plastic behind the hole. Then use autobody spot putty to fill in the void and sand smooth. Works really well.

I just ordered all the parts to do this myself. The metal parts and stug gear box should turn this into a good runner. Or I hope it does. Now I just need Mato to restock the PZ III so I can get the tank to go with the parts I just ordered!!!!!