A bit of heat works well on the gasket - nice sunny day (or managements hairdryer…)Sorry can't help with your SL but l replaced the third brake light on my CLK a while ago. It was a little fiddly but not as bad as l expected. In my case it was a case of loosening the trim inside the boot lid and reaching up behind to gain access to the brake light mounting bracket bolts. The actual third brake light was a pig to remove due to the self adhesive gasket not wanting to let go. I got there in the end though.
Yes l thought about that, unfortunately only after I'd done the job!A bit of heat works well on the gasket - nice sunny day (or managements hairdryer…)