Overflow tank or Radiator Assy replacement??

[technobuff]

My 1996 318ti with 176K is experiencing coolant leakage between the overflow tank and part of the radiator core where the overflow tank sits. I purchased an overflow tank in an effort to replace it, got the old one by wedgng a flat screw driver and pulling the plastic piece gently by the neck of the tank. Got the tank out, installed the new one in but could not press the damn thing in place so there would be no gap between the bottom of the overflow tank and the radiator core. Guess what... I broke the overflow tank by putting on the raidator cap and slamming the radiator cap with a rubber mallet. I need to know if I should replace the overflow tank or the whole radiator assy that comes with an overflow tank to eliminate the coolant leak between the tank and the core. Any help would be greatly appreciated. Not looking to replace the radiator assy if I do not need to....or should I based on the mileage of the car -176K?

Thanks, Technobuff