Mercedes SL R230 2007 boot leak not a regular leak - Help!

[roadster198]

Common leak points:
Boot seal (see Malcolm's guide).
Third brake light.
Aerial on left rear 3/4 (if fitted).
Fuel filler neck (rarely).

Also blocked drains at front corners of boot seal.

My third brake light is not sealed properly is this easy to replace?

it has clearly let water into the boot lid and has soaked the trim