The VC should be fine pretty much no matter where you get it from. There seems to be a common theme in the forums that as they get old they have a tendency to act differently, but it's not altogether awful. It sounds like the fluid cooks up a bit and starts to transfer power front-to-back at a slightly higher than originally engineered rate - you'll have maybe ~8% full time AWD rather than the originally intended ~%5 say.

I have never read one report of the VC totally failing, though I am sure this is possible. I wouldn't worry too much about a used VC, but then again I wouldn't be too worried about your current VC either - it's probably fine, though old.

The most commonly reported symptom of an old VC is a 'thumping' under the center of the car during sharp 'parking lot' turns after some straight line driving (like on the highway). I think the theory is that as the fluid gets older it's viscosity properties start to degrade, and it heats up too fast during straight line driving. So you go out for a quick run on the road, which heats the VC fluid up, which causes torque transfer. But then when you're doing 'parking lot' turns your front wheels are moving at a different speed than the rears, which when combined with a torque-transferring VC causes the typical 4x4 driveline binding putting stress on the center prop shaft. On some 4x4 trucks this causes a little wheel-hop during the same maneuvers. The thumping is the prop shaft moving around in the rubber mount just ahead of the center u-joint, and running into the limits of that soft bushing and probably contacting the steel bushing holder. That's my understanding anyway. It's not the end of the world.

I have had my bevel gear apart and rebuilt it (though I haven't yet been able to verify if it's been a successful rebuild - I'll post about it when I'm done) and I can tell you that in MY bevel gear everything was in pretty good shape. The o-ring seal around the crown ring was totally shot (hardened) and a couple of the other seals looked like they needed to be refreshed, but the gears themselves and the bearings were all in great shape.

Any trans shop should be able to do this kind of rebuild for you, but it will cost about as much as a used unit from Eerie Volvo does, and they guarantee theirs for life!

Any driveline place should be able to give you a new bearing or replace the u-joint or either the front or rear CV joints as well. They will even be able to balance the shaft for you before you put it back in.

If you're interested in fixing this and don't have the mechanical skills or time to research and acquire them, start finding your local 4x4 and transmission guys.
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1998 V70 AWD->FWD Turbo 200k+