I'm living in an older apartment building, and I've noticed that I'm losing a fair amount of heat due to a gap in my balcony doors. Specifically, the sliding glass door fails to form a seal with the frame at the top.
What's the best way to solve this? The sliding door itself doesn't appear to have any aligning mechanism that I can use. The only thing I can think of is filling the slot for the most part, and then adding some weather seal that it can push against.