I posted a thread sometime ago about water leaking into the boot/trunk. The obvious suspect was the tailgate rubber seal, however mine was alright and what appeared to be the route of the water into the spare wheel well wasn't consistent with the rubber seal being the fault. I went to my local Honda dealer and enquired what the problem might be. They told me that they had had a small number of Jazz's with this problem. He showed me a Jazz in the showroom and pointed out the sealing between the body panels around where the boot seal is mounted and said the tailgate would need removing the joints on the panels resealing, new paint plus checking the seals on the rear lamps at a cost of £350-£400.
Although my Jazz was out of warranty I contacted Honda UK explained the problem and they said they would foot the bill which they did, no arguments/tantrums. I now have a waterproof Jazz.

 

Thanks for the update and your getting it fixed for free. It is an area that one would seldom look in. I have already sealed the top of my taillights and other areas open to the outside elements.
I also filled in the large rust collectors in front of the rear wheel well.

 

On the subject of rust check out the top of the rear doors where the rubber seal sits, I've seen rust breaking through the paint on a couple of Jazz's there.