It's a fairly dense stick-on seal. Closed cell black foam self-sticking tape is available in all kinds of small dimensions. It would seal well, but may not last long. For looks, it would be hard to smoothly cut the edge at an angle for a matching look.

I'd go have a chat with a good body shop or a garage that does classic restorations and they may know of something suitable. One tricky bit is the 90 degree corner. You can cut a partial V-notch in it then fold it over a drop of hot melt glue or use contact cement to tack and hold the corner.

If whatever you find needs to be raised a bit for a better seal then I'd think about using one or more strips of a thicker, best quality you can find, double faced carpet tape as a spacer. You could use a black felt pen to help hide the beige edge of the tape.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now