So for the second time in two years the right side radiator tank has a crack towards the top of the tank. Is this common. These are such a pain to replace.
07 SS LS4

 

It certainly isn't uncommon for plastic end tank radiators to crack in general, especially given the age the OEM ones are getting to now.

It is unusual to have a second failure so soon after - did you go with another brand new factory radiator or an aftermarket replacement?

Anything unusual / under extra stress- perhaps damaged mounts or a hose that's too short or something? May have just been bad luck on your replacement.