I've seen these leaks from under top foam dam a few times. Remove the foam and you'll likely see the crack. Age, excess heat, air in system and excess pressure.
Flush, Rad, CAP, thermostat, upper/lower hoses & tees, Toy coolant is my standard. ALL OEM!
If system looks like it may have contaminated or build ups. I do a chemical flush with BG flush first thing, than triple distilled water flush. If 04 up (pink coolant). I only chemical flush if I really must.
IMHO It's not worth shop time to rebuild these anymore! But, DIY perhaps it is. May be fun and rewarding of job well done!!
Core can be taken to a radiator shop. Which will boil in a tank of solution cleaning internal, and then they soldier leaks. I took radiators to these shops, for most of my life, up to about 20 years ago. Cost was usually less than $100 of all metal rads. But hard to find rad shop still open these days, as most have closed, due to cheap Chinese made junk and raising labor cost.
Personally I stopped even recommending anything but NEW OEM. Shop time to deal with swapping and glueing foam, eats into cost saving of aftermarket. Better put money into new OEM part. Also I stopped using aftermarket, as most aftermarket have fitment issues. Some alignment with bolts holes and most weep at lower OEM radiator hose & clamp. Which then takes some custom work and or aftermarket hose and or clamp. A rabbit hole I just don't like going down with clients.
IMHO the life of factory radiator is very dependent on proper maintenance. I've one lasted for 20 yrs/360K miles. Which I bet it could have made 25 yrs/1 million miles, had it & coolant system been perfectly maintained by the book.
So when you consider a well maintained rig, could get 25yr/1 million miles. ~$500 OEM = $20 per yr/$.0005 per mile, just isn't that much.
I've about a dozen core's here now of 100 & 200 series. Thinking, "hey one day perhaps I'll rebuild them". But what will happen; I'll load them up and take to recycler when run out of room to store (like now).
