Welcome to the forum.
If you do some searching, you will find that plenty of people have dealt with the problem and it comes up regularly. There are some professionals that rebuild or reprogram the units. A few people have the experience and tools to swap or reprogram the eeprom. Many have replaced the transponder, central locking unit, and DME with a matching set from another car.
In my most recent water intrusion event, caused by a clogged drain to the left of the engine, I was able to clean and dry the module before any permanent damage was done. Getting all the water out of the carpet padding was the most time consuming part.
Here's the worst one I've had. This car sat for about 6 months, wet. Once corrosion gets into the relays, you might as well replace the unit.
