Head gaskets and intake gaskets, even on low mileage Vortecs.
I hate when poeple think that anything over 100K is "pushing it". There is a Vortec 350 owned by a kid in my class(96 Tahoe), that has 260,000 on the clock. No major engine work of any kind(actually no engine work, just accessory replacement). Heck the transmission was only replaced cause it dropped a driveshaft and cracked the case.
My 1997 C2500 runs like a champ, doesn't burn a drop of oil, no leaks, but it did need intake gaskets not long ago. That is only 105K though.
Look for service records or repair records. If things like the gaskets were replaced I would be more inclined to get it.
I won't say I would jump on it, you are right, many vehicles don't last that long, but its usually ones with poor maintenence or that are beat on their whole lives. A properly serviced and treated engine will last a long time. Mind you my stuff never lasts, and it isn't for lack of service...