I have a Canon AE-1 that I have a slight sentimental attachment to (it sat in my mom's college roommate's closet for 30 years before being bestowed upon me). Ever since I started using it, it's had this weird problem: The advance lever and the shutter seem to work perfectly while I'm shooting, but when I get the film developed, some of the photos have black on half of the print. Some are fine, and the amount of black varies. There are also a bunch of light leaks on the most recent roll, which might be a clue. Any ideas what could be happening here, and if it's worth getting fixed?