Window frame crack

[Steelsun]

Both the doors of our trailer (2014 Microlite Fragstaff 25DS) have windows with a little crack on the bottom of the frame like pictured. They look like they might be stress cracks, but I'm not sure. Or are they supposed to be there?

Our trailer is new to us and I was doing some caulking replacement on some windows when I noticed these.

Is it ok to fill these with caulk, or are they supposed to be there for "breathing" or something. They look to me to be an avenue for water entry and possible damage to the doors.

[SeaDog]

That looks like a crack from the molding shrinking I would place a small sealant in the crack just to seal out any moisture.

[Steelsun]

It's the plastic frame, kinda looks like it torqued and cracked. Both door windows have it in the same place.

I Think I will fill it in, just in case.