I've replaced that molding on many Space Invaders and Space Invaders Deluxe. It is slotted. I don't recall it being glued in, but it's been awhile. I do remember this....it's not a standard size. In fact, I would say it's been "trimmed" at the factory. If yours is like the handful I've done......look at the outer edge of the molding. You should be able to see a "blade" cut all along it's edge, where it was trimmed down. The outer edge of the molding doesn't match the inner edge's contour. Standard textured 3/4" molding will overhand a hair (or two).
Edward