Joel! You're certainly right, even I can see what it is now !
That gap: I would go for white Milliput (kind of a sculpting epoxy as you suggested yourself!). The advantage with Milliput is that it can be smoothed with water, I use a rubber tipped sculpting tool (looks like a paintbrush but with a rubber tip instead of bristles) and usually end up with a good joint and a minimum of sanding. If you don't feel like running to the art store, an ordinary plastic eraser can be cut into whatever shape is suitable and then be used as a sculpting tool!
I'm going to take your advice and go for an acrylic type putty that I can buy at my local Art store. My Milliput was so old, it just dried out, so I tossed it.