I have the exact same issue on my 01. Had 2+" of rain yesterday, than 4 degrees this morning. Have had to hit my door/latch with heat gun twice today. For it to only freeze up again and now I am just letting it sit till it warms up. Using my diesel dump truck! BullS*$% that the doors of a German designed car freeze and you can't even get in it. Is the "plug" you are all talking about that little black on on door jam? Take that out and spray WD in there?

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Dave S.
Northeast
2003 4.6is
2005 E53 4.4
2003 E39 Msport(a REAL ONE!)
1959 Fiat 600