A good radiator shop could replace the plastic tank (or both) on your radiator, but they are tricky. I have a friend who owns a radiator shop and he often breaks down the plastic radiators and repairs/replaces parts. If not done right, there will be leaks at the plastic/aluminum joints. This is the same guy I have do my brass radiators.
If it were my call, I'd opt for the OEM replacement rather attempt repair on the plastic.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.