Coolant leak?

[X5DINAN]

I know, I know, another coolant leak post.....lol
My truck has been running pretty good the last 3-4 weeks now.
But I have been noticing a small puddle of coolant directly under
the center part of the cover. I have a expansion tank on order and
all other components look good (hoses, rad, valley pan....). Do you guys think it's probably the water pump on it's way out. When I last checked,
there was a bit of coolant around the water pump, but not enough to
justify the leak?
This leak is usually when the car has been sitting over night and I'll notice
it the next day before I leave for work. And this mostly happens when it's
a chilly night? Maybe because the gaskets are hardening? I don't know?
I usually have to add about a cup of coolant every 2 weeks..
"Water pump" culprit??