If you are searching for the trim for windows, try Marine Glass Specialties. I was able to get the window channel for the side windows and that helped a lot with the leaks.
I would not recommend caulking the corners where the plastic trim is as that is how the water will flow out when it gets behind the trim. If you have leaks, you need to seal around the outside of the window channel and if still leaks, then need to remove the trim, check the screws and seal anywhere that looks like it is compromised. Then re-install that trim. I so far have not had any leaks under the plastic trim and don't want to try and remove it unless I have new to replace it with as I am sure it will just crack up .
If I ever tried to remove it for some reason, I would do it in full hot sun on a 98 degree day to hope and pray it would not break up the plastic if can't find new. However, I think Marine Glass has it.