excessive sulfur odor on 2007 model year Yaris

[death is my gift]

So I went to the dealer and dude crawled under my car and said it was a plastic bag that had melted to my whatever-it's-called. I didn't believe him so I crawled under there with him and told him to show it to me. Sure enough, he was able to scrap a bit of it off with his ink pen. I asked him what I should do and he said either let it burn off by itself or take it to a "car wash" to have them scrap it off for me.

I then showed him the printed out TSB and he said that wasn't on "all" 2007 Liftbacks, just some. I told him I wanted it changed anyway and he said they could evaluate it (whatever that means) and if they don't find a reason to change it they would charge me 70 bucks for the evaluation. But, if they did find a cause to change it they would do it for free. I told him I would wait and see if the smell went away.

What do you guys think? Are they obligated to change it even though he said, "Not all '07 Liftbacks were affected?"