Or maybe http://www.classicparts.com/1947-51-Door-Latch-Spring/productinfo/18-575/#.VNwRSc9d7X4 ??? Never tried one (yet), but it's a cheap fix if they work. Mine aren't sagging though. I could throw in a comment about the missus here, but I won't.

"When I rest, I rust"
1951 3100 5 window w/ '56 235