Replacing side flasher ('repeater')

A couple of questions.
1 Has anyone successfully replaced their side flasher (on the wing, about waist high) without taking off the plastic body trim under the wheel arch? How did you do it?
2 How thick is the rubber gasket between the chromish flasher body and the car wing?. It’s missing on my replacement and I want to make a new one from sheet rubber or neoprene.

Also, My 1988 (built 1987) XJ40 has the flashers a bit below waist height on the wing, (not in the side of the bumper). I’d like to ask what the two little chromish spigots are for either side of the little bulb. Are they just to space the orange inner ‘lens cap’ or do they get squeezed or pressed in order to get the bulb out? How does the bulb come out? It looks like a simple bayonet in the Jag parts book diagram. That is push down and twist to remove?

Apparently the bulb is a bayonet though may be rusted solid. Re my first post, have addressed this in the thread ‘Sidemarket [whoops] lamp’!