Huw - I also worried about water. So for the interim, I got some black electrical tape, punched round pieces and stuck them on. I don't imagine this will last ages, but so far so good. Am still looking for something with better glue than electrical tape. Maybe some gaffer tape will be next. The electrical tape has the advantage it's cheap and I can at any time replace the odd patch that falls off if it does happen, plus the color and texture is a dead match for the matt anodizing.