<p>Thank you both for your helpful responses. The streak is in the same location, and as you suggest Greg, the only change is that its intensity increases. I shall have a look over it to see if there's anything missing, and if not, hopefully some tape will do the job.<br /> UPDATE: I happened across someone experiencing a similar issue. I shall use the image they provided to elucidate what I reckon the problem is with my camera.<br /> <img src="https://ec.yimg.com/ec?url=https%3A%2F%2Ffarm3.static.flickr.com%2F2494%2F3915543179_bc7ac46458.jpg&t=1429627817&sig=WkcSbT9VscCwicIN8PtuKg--~B" alt="Zorki 4 - light leaks" width="500" height="333" /><br /> It seems as though my camera is a just a little bit loose in the same gap as fig. 1 in the above image, only around the front and at the top left (above the self-timer). There does not appear to be any screws missing, and simply pressing down firmly on the top of this area closes the gap. If this is all that is required to prevent this issue from persisting then I certainly am lucky. (Apologies for the double post - the image url didn't paste properly the first time)</p>