Some garage doors are.
Garage door frame rotted.
With time the wood frames and bottom starts rotting and breaking down.
The main cause of rotted garage doors is water damage.
Mix polyester wood filler or bondo wood filler and press it into the recess with a putty knife.
These dark spots are caused by the growth of fungi as they feed on moist wood.
In case you have had a plumbing accident water in your garage will move to your garage door.
Drafts around the exterior door.
Pry on the crowbar to lift the trim and loosen it.
Then coat the rotted door frame area with wood hardener as shown.
Usually mold or wood rot is easily recognizable by the telltale dark soggy patches that form around the door frame.
To repair rotted door frame first remove rotted wood with a 5 in 1 or other sharp tool.
But there are several less obvious symptoms you should be on the lookout for such as.
How to use epoxy on wood for repairs.