I have a '83 300D. When the temp goes below 30 the door locks freeze. I've tried spraying wd-40 in the lock hole but it still freezes. Any remedies?

I had that problem too
 

I sprayed Boeshield T-9 into the locks. Boeshield is a teflon impregnated wax in an spray can. It was developed by Boeing to lube hinges and the like on aircraft. Boeing was concerned about the dirt pickup associated with grease. Anyway the T-9 works great on locks (and bike chains). I buy it at West Marine. I also use it on my power antenna because it doesn't show.

I've had that problem with all my MBs up here in Canada during the winter. Especially after I wash the car.

I've tried many lubricants but none seem to work. I'll try the Boeshield if I can find it. I currently use a butane jet cigarette lighter that I carry with me (I don't smoke). I insert a 'dummy' key (4" slim metal rod)into my lock and heat the key FROM A DISTANCE with my lighter. Works like a charm. Don't know if I'd recommend this to anyone, though. Whatever you do, don't try and force the key! Usually one of the other locks will work - try the passenger or the trunk lock. Either should open your car if the locking system is similar to mine. My mechanic also recommended blowing out the lock with compressed air to get rid of the accumulated moisture. I've done this before and it seems to help.

http://www.boeshield.com/ I am sure this will do it, I use Super Lube spray and grease on on almost everything I have found it to be a necessity in OR's because of the super dry air and saline solution all over the place. I am sure a bunch of people would flame be on this but WD-40 does great at breaking stuff loose, you can tell by all the black crud running down the side of your car, But does not hang around to keep everything happy, happy. The other good one is Rem Oil (you can find it at gun shops) I think that is a super product. I am always looking for a good lubricant for equipment and I am giving this boesheild stuff a try as well.