What year trailer?
Once we determine the brand of window you have, I'd just go to an RV dealer with that name and see if they have a replacement part. I seem to recall those things are pressed together and while you may get it apart, it probably won't be real strong if you were able to fix it and reassemble. I wasn't aware of any bearings in the windows though.
If the window is easy enough to open from the outside, make sure to secure it before you tow so that passing vehicles don't pull the window out and possibly cause damage.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR