... because instinctively I would have said that the CLU is under the driver's seat
I have had some luck with wet CLU, in bringing them back to life.
Remove the seat and disconnect and remove the CLU box.
Open the CLU and take out the printed circuit board (PCB).
Put the PCB in a plastic zip-lock bag or in a shallow pan and pour in 1 litre of isopropyl alcohol.
Shake so that all parts of the PCB are immersed in the alcohol.
After a few minutes, remove the PCB from the alcohol and let dry.
The alcohol will draw out the water and then completely evaporate, leaving a dry PCB.
Reassemble and good luck.
This works depending on how long the CLU was exposed to water and possible corrosion.
Happy Boxstering,
Pedro