These older figures are prone to cracking. Like The Skull said don’t leave this one with bent elbows.
Fixing it doesn’t seem possible without making it look bad. If looks don’t matter you can look into using a small amount of rubber cement in the crack or spray can flex seal on the entire joint. I wouldn’t recommend it though.
I'd get some silicone oil and apply it to the damaged rubber. It won't repair the tear, but it should stop the rubber from drying out any further and tearing more.
Ultimately though, it's just a function of the cheap materials HT use.