Just in case you don't know this....if the key in the trunk lock is turned to the right it will stay locked and unlocking the car at the doors will not unlock the trunk. Make sure the key cylinder in the trunk lock is turned to the left and remove the key so that the slot is vertical .

Aslo, one of my 300e trunk seals was replaced with an aftermarket seal and at times it seems impossible to open. I thought I had a lock proplem but using maxumun force opened it. I sprayed the seal with ruber silicone rubber conditioner and it's OK now but if the trunk stays closed for extended periods it is again very hard to open as the seal sticks to the trunk lid.

hope this helps,
Acky