is there a hole in your shutter? not uncommon, easily caused by sun (camera on back, lens cap off).
not too difficult to repair small holes, or just keep lens cap on apart from taking the picture, to minimise fogging the film. of course, that may lead to some "forgot to take the lens cap off" blanks...
lovely!
easy enough to check when changing film, just hold it up to a light with the lens cap off.
if it's only a pinprick, it's only enough to show if you happen to have had the lens cap off for a long time between shots, or it gets some direct light.
is there a hole in your shutter? not uncommon, easily caused by sun (camera on back, lens cap off).
not too difficult to repair small holes, or just keep lens cap on apart from taking the picture, to minimise fogging the film. of course, that may lead to some "forgot to take the lens cap off" blanks...