Hi everyone, just wanted to say thanks for all of your tips. I
especially like the air compressor idea, and I'll keep that in mind
for the future.
The key I have is the master key, so that wasn't the problem. I went
to a local MB dealer and they tried WD-40, but that didn't work and
they also referred me to a locksmith...so I figured that was the only
way. The locksmith made another key and then just turned it really,
really hard (using a wrench to turn the key with more force) and it
worked. Unfortunately, the stuff I thought was in the truck wasn't
there...but that's another story.
The lock still doesn't work correctly, but at least I have an extra
key and keep a wrench in the car for the next time I need to open the
trunk. I'll just add that to my list of "things that need to be
fixed". Fortunately, that MB is not my primary car...so not having
trunk access isn't so crucial. There are plenty of other things that
need to be fixed first.
Thanks again for all your help!!!