Date registered: Jan 2004
Vehicle: 2010 E350 P1/P2, 2008 S550 Designo, 2002 ML320
Location: Aridzona, USA
Mentioned: 1 Post(s)
Quoted: 108 Post(s)
I've got no SL currently, however the 'popped open at highway speed' reminded me of the description in my W221 manual. The Emergency inside release (green button in my car) can be opened at any time, including while at speed. Perhaps there is something going on with that switch in your trunk?
Good luck with this, I recently went through the drama of having someone close my trunk while both batteries were disconnected. Only afterward did I find out the mechanical key lock was toast! I had to cut a hole in the spare wheel tub (plastic) and reseal it after reconnecting the consumer battery ground strap.