Easy Fix and it's less than $4.00
Seems like you have a forming crack in your radiator neck and unless it is severe I think I'd opt to get the most miles out of the current radiator I already have. Besides the $300 you don't want to spend on the new cooler, JB weld will fix your problem most likely for years to come. I've used this great goo epoxy on everything from metal to waste water holding tanks and everything I've used it on is still in operation today. Unless you just like spending money on engineered defects, I'd go with the JB Weld and correct the problem instead of buying another that will fail the same way.
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan