I picked up a used driverside switchplate to replace the malfunctioning one after I got it wet. What I found interesting is that the bottom of it is designed a whole lot different than the OEM installed in 1999. I suspect this was to address the ones that got wet and then rusted. The newer switch control's bottom is completely open.

 

On the part #'s, are they numerically listed something like this 123456789 AA, 123456789 AB? The latter letter signifying the newer version.

 

I don’t know if drainage was the idea in the manufacturing process as much as “cutting costs and using less materials” was more likely because.... you know... it’s ALL ABOUT THE PROFIT!!