I couldn't find any rubber glues from brands i trust, so i got myself bison glue max repair, it's elastic and should work on all materials. I've used it to glue the skin back together at the neck, and luckily it can be removed again with some care once i have to do repairs again. It's almost as nasty as the original glue on RB's though, but i don't know how flexible it truly is since i haven't used it on any tears yet. I've heard many people say it, but i wouldn't advice using regular cheap superglue. Especially not on tears. I wouldn't expect it to last very long.
Do you have any spare pieces of pleo skin or any other similar type rubber? If you remove the skin completely and melt or glue the spare piece onto the inside of the skin onto the tear, it should be good as new and just as stretchy, unlike glue.
If you don't feel like skinning your pleo for a small fix, glueing it from the outside should do the job as well, but make sure you get a decent glue.
Just do whatever feels best to you, we're all just figuring stuff out.