t-slot type weather stripping for white vinyl casement window

You are just looking for the top seal, right? I don't think the seal in the bottom image can replace that. That appears to lock in using two tabs, while yours locks in using a single "T" insert.

See our 58-135. Its dimensions seem similar, though its a bubble rather than a fork. That may not make much of a difference, though. Could you use this as a substitute?