If I remove the indicator windows do I need a blanking plate of some kind to stop water etc getting in?

I haven't bothered and a couple of years on they still work. One is missing half the remaining case as well following a crash.

I am rather surprised. A testament to their quality?

Not much water gets there and it drains out easy if it does. I think. Well greased too.

My '09 ones had the blanking plates hidden under the window housings. Lovely.

There's a blanking plate on the back of the indicator. Just reuse one of the indicator screws to fit it.

No joy no plates there must be too old.

If they look like this then covers are available. If they are older then a bit of tape will have to do the job.