Be glad they did not try to use white duct tape to fix a leak. I have seen this.
Do it yourself. Minimal tools and skills required.
Remover the window by unscrewing the phillips (or square taper) screws from the inside. These should be visible in the window frame. Window will likely not fall out, it will need to be pried out, use a putty knife or something that will not bend the frame or damage the siding.
You will see a lot of looks-like playdough. Just peel this off everything.
The butyl window stuff, mentioned early in the forum, is what you need. Any and all RV shops should sell this.
Place it along the permeter of the window the same as where you took it off. This is what makes it waterproof.
Put window in, have someone hold it now.
Screw things back together.
The putty will ooze out as you tighten things. Work the screws tighter and tighter a little at a time and go around the window on each screw a little each time until it is tight. No need to over-tighten.
With something plastic, like a plastic knife, trim the excess ooze away from the trim. OK to wait to do this the next day since it will ooze many hours after install. Or OK to never trim the ooze out, wont hurt anything except the looks.
Or have the dealership do the repair and expect a carp job that will likely leak again.