I have corrosion on about everything on my bike. It sees a LOT of bad weather. I do have one coil that has some rust on it. It happened to have mud and stuff packed up around it on the valve cover. In my case I don't think it is water getting into the wells but condensation that naturally happens with heat cycles and that particular coil could not breath well with the mud packed around it. It looks like to me that the offset gaps the coils have on the sealing rings is for excess pressure to relieve itself when the heat cycles happen. the umbrella on top is to keep water out. I could be wrong though. I have checked my bike over pulling into the shop after riding miles in a monsoon and the valve cover it always dry. It is dirty from stuff hitting it but the heat takes the water off almost immediately. Just my observation on my bike.