Window frame seal on A.R.E cap.

I bought a used ARE fiberglass cap and while prepping it for paint I noticed someone had put some silicone on the top of the window frame, I’m assuming they were trying to fix a leak. Anyway, I removed both frames to reseal and discovered ARE used push in bulb seals. Although the seals are available I’m wondering if I would get a better seal if I used butyl tape instead of replacing the rubber seal?

 

which window is that

 

It’s the frame for the windoor on the right side but I discovered butyl tape won’t work because the gap would be to big