well today I went to replace the bulbs as they were showing white light.
initially I tried pushing them to the side to release them and I heard a snap and something fall down inside the wing (the wee plastic clip broke on the indicator).
I then thought bugger it ill take the wheel off and wheel arch liner out and get to it that way (which it appears is the way your supposed to do it).
taking the wheel off and liner out was pretty straight forward but when I got the liner out I noticed this immense amount of mud behind the liner which was the same on both sides of the car. I'm pretty sure that's one of the main reasons that the bottom of the wing has started rusting on both sides.
I cleaned it all out and hosed it all too and its all clean and shiny now just waiting for the new indicator so I can replace the one I broke.
i would definitely recommend checking your cars and giving them a clean to try and prevent rusting if nothing else.