Dry graphite is best and what experienced/knowledgable locksmiths use (and have far more experience with locks than a MB technician). I've used graphite for years with no failures. However, why don't you call your local MB service dept. and ask what they recommend so we will all know.

Good luck.

Tom

__________________
America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
Technical Advisor to Am. Honda;
Supervisor of Maintenance largest tree care co. in US for offices in Tex.