The copper sleeve insert you refer to is intended as a preventive measure since these plastic radiator necks are so fragile. I have used it on my 560SL. The insert arrangement however, will not work for a repair since the sleeve must be epoxyed in place and the heat related expansion/contraction will cause the crack to reopen.

I'm afraid a new radiator is in store for you. After you get it, go to your closest big-box hardware store and buy an internally snug-fitting copper pipe nipple to epoxy inside the upper radiator hose connection. Can't help with the expansion tank connection. I will say however that most people tighten those hose connections way too tight. Not necessary.