had to top it up and it leaked down the side. would sanding help? and if so what grit? I will be using an acrylic sealer spray after and it may even it out a little. This is for someone I don’t want to have to make this die again but will if I have to.
So it looks like one of the sides is concave, yes?
If so, I would fill it in with a doming resin overfilling as best as you can without it spilling over the sides. The resin will contract a smidge when it cures (as it cools), so hence the need to overfill it just a bit. (You want to make sure it domes.)
Once you are done, yes you can sand it. I would suggest starting with a 400 grit wet/dry sandpaper, then working down to a 1000 grit or higher. You can see the techniques I’m talking about in this video on the Resin Obsession youtube channel: http://www.youtube.com/watch?v=51kSn5Xqfw8 Once you have finished sanding, finishing with an acrylic spray should give it a glossy surface.
If you remember, could you share a picture of your finished die?