As counterintuitive as it may seem, the key to a long(er?) term fix is to actually widen the crack! 1/8th to 1/4 inch.
I used a Dremmel Moto-Tool to enlarge the crack, actually using a drill bit at the ends of the crack (most of which are right up front on top of the radiator where the return hose flairs into the tank) which is often stress-related. Using one of the cutting/grinding bits down the length of the crack allows room for the radiator epoxy (mine was a small Tootsie Roll-shaped) goop that you knead for a minute or so, until it was a uniform green) which you push through the crack so it will MUSHROOM behind the plastic. Of course it needs to be warm, dry and grease & anti-freeze free 1st.
After this stuff dries and hardens you can use a couple of overlapping layers of JB Weld to reinforce the repair.
Mine has lasted over 6 months... Got me to the 120K timing belt/water pump service. Too bad I ordered and bought a new radiator prior to this last fix, though.
Well, at least I'll have a spare
Good Luck!