Bubble seal
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It's tough to say what you have from this photo. You mention that the part that goes into the window track is 1/4", but I don't know what style it is. There are a bunch of different methods of inserting into a window track. Do you have an undamaged sample that we can see? I know it's deteriorated, but please try your best. Without an intact sample, I don't think I'll be able to narrow it down.
I have no idea what might work. Without knowing what the shape of the weatherstripping is, I have no reference with which to even guess. It really is important that we see an undamaged sample. Without one, it's not possible for us to narrow it down. You could have anything.
I recommend looking at our complete selection of bubble seal here. You may find something that looks familiar.