Ironman 4x4 Breather kits are crucial if you're taking your Jimny through any sort of water that may cover the entire differential, transfer case or gearbox. Water getting into those areas will turn the oil into a white milky substance, and can will cause failure if not changed quickly.
Note: For full protection, two kits are needed. (Front/Rear Diff + Gearbox/Transfer Case)
Ironman Breather Kit