It can't be a huge deal - I've never even heard it mentioned on the forums. Maybe he was thinking about cavitation - which is a big deal in the 7.3's when the antifreeze is not correctly maintained.
Yeah, I would agree. He's probably thinking of the cavitation issues. But, keeping up with radiator flushes and having the right amount of additive in the green antifreeze pretty much eliminates that issue. The only things I would caution you on would be if it has been run with a chip in it, did it have gauges in it? What about maintenance records? Any leaks anywhere (water pump, radiator, oil, fuel)? How is the turbo on it? How clean is the air intake? How strong are the batteries? If you have to replace one, it's best to replace both at the same time. I believe the rods in the 2001 and up 7.3 l are PMR instead of forged metal like the 99-2000's, so, if you plan on modifying it with a big increase in hp, be aware that you'll probably have to consider replacing the rods. And, the 2001 automagics had the mechanical diode issue, but you said the one you're looking at is a stick. I say go for it, if the price is right.
And, welcome to The Diesel Stop. You'll get info that you didn't even know that you needed to know off of this site.
just my .02 cents worth
Y2K F250 CC PSD Auto, Short-bed Lariat, Woodland Green/Gold, ordered 07/10/99, born 09/12/99, delivered 10/08/99, BAK RollX bed cover, Bed mat, Zoodad mod, Viper Remote Start Alarm, Fumoto valve, undercoated, 139k somewhat error-free miles (so far) [never back to dealer for anything] , Edge Evolution (60 HP setting), Pioneer DVD/CD/iPod/XM satellite
Repairs: CPS, Water Separator Valve assembly, rear axle bearings, VSS, batteries, brakes, alternator, serpentine belt (x2), all 4 power lock actuators, water pump, air conditioning lines, battery cables
2009 VW Tiguan 2.0 l turbo 200 hp gas engine Wifey's car