Appears to be windshield gasket and possibly sunroof combined. I don't have sunroof and had rust there caused by windshield leak. It's a cut-out and replace kind of repair (internal rust), sorry. If it's the truck you want at the price your willing to pay the go for it. Look closely at the rest of the truck first, the floorboards and firewall around the hinges 
Thanks!
Yes, I really like the truck but the price I was willing to pay was dependent on the cab and frame being rust free. It has the typical rust in the bed (though much less than a lot of trucks including mine) and that's NBD to me as I have a complete rust-free and straight bed just waiting for a truck to put it on.
Since the owner's not willing to come down in price I don't think I can buy it. He'd need to knock a good chunk off my initial offer to make it worth it to deal with that rust. There are other extended cab trucks out there that maybe aren't in as good of overall condition but don't have this kind of rust for less $$.
