Trunk will not open with trunk pull,opens with key only

A repair shop would use a smoke generating machine (sold by Matco, Snap-On, Vacutech) these machines are expensive but are used to find vacuum leaks and test for leaks in Smog test stations. This may sound funny but years ago when I was an apprentice mechanic my boss sent me over to an old mechanic in our town, we had a vacuum leak we couldn't locate. The old (and wiser mechanic) lit a cigar, inhaled and blew the cigar smoke into the vacuum line a few seconds later cigar smoke leaking from a vacuum hose behind the dash quickly identified where the leak was. In your case and I am not very familiar with Mercedes but look for where the vacuum hose brings vacuum out to the door or trunk lid as the opening and closing of the doors and truck lid could cause fatigue of the vacuum line.

Epoxy glue, or silicone using care.. Allow to set thoroughly before driving or starting.