Well after thinking my driver's side repeater had gone, I noticed when setting the alarm the bottom of the wing flashes! Upon closer inspection it would appear the bulb holder has fallen inside the wing. Apart from taking the indicator off and getting a coat hanger in there (my first thought), how would I get inside the wing?

 

Can I access it by taking the arch liner off?

Yes, you can access it via the inner wing. undoing 2 or 3 screws would give sufficient access.

 

However you should be able to access it via the indicator hole. The wire runs close the hold itself.