Century Wave Master Repair?

[MikeMartial]

So I purchased a Century Wavemaster, used, from my TKD instructor.

Before I bought it, it had developed a leak where the base narrows to the neck; it was repaired quite well by someone familar with plastics.

It seems to have started leaking water again at the same site...

.....any ideas/experience with this?

I've emptied it, and will probably just fill it with sand. But I'd like to reinforce the weak area, somehow.