Your windows are probably made by Kinro. I believe Lippert bought them out several years ago, so the "parts trail" is probably difficult to follow. That said, Trekwood.com has several "window operator assembly kits" on their website. Here's the link to one for a 2004 Montana:
https://www.trekwood.com/products/10...cify-Size-Type
If talking with Trekwood fails to get the parts, you might try Lippert Customer Support. As I said, they bought the manufacturer and may have parts available, but we're talking a 16-17 year old trailer.