Help! I just sold my Korg DW8000 but the person who has is tells me the last 8 keys go dead after just a few minutes of play. Has anyone ever heard of such a thing? Any ideas what could be causing it?

Maybe he has accidently created a key zone?

The DW doesn't let you create key zones; that first came about with the M1, so it isn't that.
If just that one octave is dying after a few minutes of play, there could be a leaky capacitor involved. If there's a bank of them with a capacitor dedicated to each octave, it could be crapping out and leaving that one section with no juice.
That's kind of an old-hat problem you'd only tend to see with older keyboards, though, so its more likely that a CPU or co-processor is going fuzzy in some way and you can't diagnose that at home unless you're way up there in digital array repair!
Take it to a tech and BE SPECIFIC about the ailing area and behavior. If its just that one section, there may be a relatively easy fix for it. Sometimes a company no longer has those custom chips available and you're simply screwed, but just as often, its a quick fix. Hope its the latter; the DW rocks & I'd hate to see it lost.