Andy, I'd say it's not the news you want, I'm afraid. I picked up an ace IG-88 Trilogo from Nick at FF and it's similar in that there is the tiniest tear near the seal (outside on this one) and similar suspect seal at the bottom of the card but otherwise brilliant. I know where you're at though: it's too good to be a reseal, surely?! You have to ask yourself what other logical explanation is there for the damage under the bubble, the slightly wrong seal and the pencil marks on the footer and there isn't one.
How much is it worth as a reseal? Always a tough one. I don't know what it's worth as a MOC or how desirable it is. In my mind a reasonable reseal should be around 20% of the real deal (for Kenner and Palitoy). However, that's not an average reseal, it's almost flawless. I'd say you'd be safe up to about 50% of the full MOC value, maybe a touch more.