mishimoto question.

There return policy is:
1. contact distributor, who will send you warranty form to fill out.
2. Fill out form, including proof of purchase and credit card #.
3. A new radiator will be shipped, you will be charged shipping cost of radiator.
4. Replace radiator and return bad unit in box.
5. They will charge cost of radiator to card if not received within 30 days of sending out replacement.
 
mine's leaking... can i use some stop leak in it without ruining it?

Definitely not.
You essentially have two options. You could do as others have suggested and try to get a replacement under warranty. Alternatively if the leak is small and you can't wait for a new radiator, you could go to a radiator shop and have the leak brazed. Should be an easy repair since it's aluminium.
 
well i contacted mishimoto. i had to fill out a form. they charged me ten bucks for the shipping to send me a new. then i send the old one back once it arrives. luckly i still had my OEM radiator so i swapped it back in and thats work for the time being.
 
You did what I would have done. I was going to suggest buying a cheapo "hold-over" radiator to use until your replacement arrived. It's good that you still had your old one.