Coolant leaks when it's really cold

[Coronado126]

The water pump housing isn't starting to get grooves or any signs of wear right?

While I've never had this happen, Cummins does say that use of petroleum based lubricants will cause the oring to swell and leak. All the products lubriplate makes are petroleum based that I've ever used.

You might try it again a silicon based non petroleum grease. I like Sil glyde. It's made by AGS but Napa rebrands it and sells it under their name as well, but anything non petroleum lubricant would work.