Rain detection works perfectly, and I have not yet noticed any corrosion. The only thing I have noticed that really needs to be changed is the following.
The rain sensor only updates at certain intervals, i.e. even if it rains and the sensor gets wet, rain is not detected immediately, but only when the update cycle has expired. This could be problematic if, for example, an awning needs to be retracted immediately.
Good to hear! The corrosion probably won’t show for many months, my stock-standard detection PCB lasted 6+ months before constantly reporting it was wet.
Agree the slow updating could be an issue. To overcome this I switched to a custom raindrop sensor connected to an ESP32 and used a combination of an analogue sensor using platform: adc to detect a raindrop (making a momentary connection between two probes), and then a binary sensor using platform: analog_threshold to elongate the detection to a minute or so. This way, the first drip (from a few collected drops 
) tells me it is raining - and a lack of drips for at least a minute or so tells me “no more rain”.
Only tested for a few wet days so far, but has worked well.
We had periods of light rain last night, and my custom raindrop sensor provided moisture detection around 20mins prior to the initial rain gauge increase (tipping bucket type, measuring 0.2mm per tip).