I'm with synthparts on this. Every 106 will eventually suffer from dead 80017As. Mine looked as if it had recieved very little use with previous owners, but within a year of purchase, one chip failed. Another failed a few weeks later.
I wouldn't consider buying another 106 (or MKS7, MKS30, etc) unless all the offending chips had been replaced with clones, or it was cheap enough to cover the cost of their replacement. A lsiting may say "fully tested, 100% working" - and that is quite possibly true, but it could still fail tomorrow!