canon ae1 light leak?

[fingerprints]

i've got a bit of a problem. i've got an old canon ae-1 that is my main 35mm camera. i love it, and i am very happy with it, but every once in a while i get a couple pictures that have light damage on them. most recently, i had two pictures on a roll of 24 that were damaged. the one attached was the worst photo on the roll hit, and luckily it was just a bad snapshot of the dogs playing, but sometimes it hits otherwise great pics. on this roll, the affected pictures were 6 shots apart. the other shot was faintly affected.

anybody have similar problem? i'm poor, and i don't know of a place to go that can do a camera check up for cheap or free. i'm assuming i have a light leak, but i don't know exactly where and how, so i'm curious if anybody can recognize the pattern and tell me what i need to fix. am i maybe changing lenses incorrectly? or if anybody knows someone who'll diagnose my camera illness for free in the Los Angeles area, feel free to advise.

thanks!
joel