Window Replacement - looking for source or advice

Since it's leaking between the glass and the frame, you should be able to have the glass reset in the frame rather than replacing the whole window. An RV repair place should be able to do that. (A glass store probably also could, but many of them are not too well versed in RV window construction and in any case would likely not have the necessary scaffolding etc. set up to perform the work and so would have to charge more.)