Every one of them has a serial number on a sticker located on the lower tank near the bottom facing the engine when installed. You have to pull back the rubber flapper seal to see it.

 

So I bought this radiator on Ebay back in march its still under warranty. I got in touch with the seller......I sent him my leak pictures, he emails me back with" GET THIS"
I spoke to my distributor he tells me you should deal directly with CSF about the warranty issue.....I replied back I don't have to call CSF I bought the radiator from YOU!...
So I called CSF and I emailed the leak pictures to their customer service.....They sent me an email and told me due to the fact that I did not purchase the radiator directly
from CSF They cannot honor the warranty and I must deal directly with the Ebay seller......So I emailed the seller and I told him I don't have time to play this game of you
pointing your finger at CSF and they're pointing they're finger at you I bought this radiator from you!!! I need YOU to handle this Today.....He emailed me back and told me that
he is not pointing any finger at anybody and that he's dealing not only with me but with CSF and his distributor.......I replied that's your problem your the seller and I'm filing
a complaint with Ebay, PayPal and my credit card against you......My credit card issued me a credit while they go after this guy.....and now I gotta buy yet another radiator.

 

Latest update.......while the eBay seller and CSF point fingers at each other I bought this plastic tanked
foreign made radiator to get by on. WISH ME LUCK!!!

 

They repair aluminum radiators all the time. Should be no problem, especially if you have already found the leak and have the radiator removed form the vehicle. Try another repair shop, not necessarily a radiator shop but a weld and fabrication shop. The radiator guy may want to sell you a new one more than fix your existing one.
Also, I've actually had some success repairing the plastic tanks on the newer radiators using Marine Tex epoxy. They say JB Weld may also work but I haven't tried that. Half the time the Marine Tex has held up. The problem there is any epoxy you use does not have the same thermal expansion and contraction properties as the plastic tank and ultimately after a year or so it may start to leak again.
You may also want to consider putting some thin A/C line foam rubber between the radiator top tank and the front wall. I did this to mine and haven't had any radiator problems in 80K miles. This is typically where the plastic radiators fail because the center mount provides just enough movement for the tank to rub against the front wall seam when you hit any kind of road bumps.

 

^^^^^This, Doc Knows!