First of all, do not try to repair the gearbox yourself. A gearbox is a very complex mechanical system that requires specialized knowledge and skill to repair. If you don't have enough technology and experience, repairing the gearbox yourself can lead to more serious breakdowns.
Second, don't continue to use the gearbox in question. If you find that there is water ingress into the gearbox, you should stop using it immediately and send it to a professional repair shop for inspection and repair as soon as possible. Continued use of the faulty gearbox could lead to more serious failures or even complete damage to the gearbox.
Finally, don't neglect the maintenance of the gearbox. The maintenance of the gearbox is very important to prevent many failures. Regular replacement of the transmission oil and filters according to the manufacturer's recommended maintenance intervals can ensure the normal operation of the transmission and prolong its service life.
In short, if you accidentally let the transmission get water, be sure not to try to repair it yourself, continue to use the faulty transmission, or neglect the maintenance of the transmission. The correct way is to send it to a professional repair shop for inspection and repair as soon as possible, and maintain it according to the maintenance interval recommended by the manufacturer. Only in this way can you guarantee the proper operation of the gearbox and extend its service life.