I have the same problem on my RT 210P, on the driver's side, but not nearly as severe as yours. I've tried a couple solutions but really still have to over tighten the crank to seal the window. I replaced this crank four years ago when I bought the RV and that did NOT solve the problem. As booster wrote, I believe the best solution is exactly what he suggested. In fact, I will be implementing his suggestion on my window this fall.
I'm actually on vacation now visiting my son. Along the journey the crank to the rear window on the passenger side failed. Having ordered a set four years ago, I had the new crank for this window with me. So I replaced it yesterday. After seeing this post I sat down today and put together a guide, with pictures, on what I did to replace the crank on my '08210P. Hope the attached helps someone.