Well, it looks like I may have a remedy, even if it might be short-termed.

Yasterday afternoon I sprayed some silicone spray lubricant in and around the door latch. I mean, really got in there. Stuck the straw up, down and behind the latch and into the door. It immediately felt smoother in operation. This morning it was -10C and it worked just fine.

Maybe it's still a problem that needs attending to but it looks like the major annoyance has been removed for now.

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8/2011 X5 xDrive35d Sport, Black Sapphire Metallic, Black Nevada Leather, Fine Burr Walnut Trim
2/2001 M5, Jet Black, Exclusive Complete Black Walk Nappa Point Heritage Leather, Black Cubic Trim