tips about repairing a japanese tub

Thanks you for your mail.
Hinoki tubs do not leak unless there is a crack in the wood.
Cracks are caused by dryness. They can be repaired with a sealant:
1) simply clear silicon: it allows movements of wood and it becomes invisible as the crack closes again after normal humidity level has been restored.

2) epoxy putty: it is water resistant and with color similar to wood. But as it is hard, wood balance becomes altered.

Another cause of leaks is poor joint construction. There is not much you can do about it apart for caulking all the inner corners (floor and walls.)Use mildew-proof clear silicon.

It is very difficult to disassemble the tub and most surely you will have to replace some parts. It might be worth the work if you create double tongue/groove rims at every joint but again, the main problem is whether it can be taken apart without damage or not.