Tap the frame at various points with a screwdriver and make sure there's no frame rot if you think it's been neglected at all. Pay attention around the area in front of the rear crossmember. Around the rear shackle. Also around the power steering up front.
If the vacuum disco is intermittent its probably not that big of a deal. You could go to a posi-lok for about $200 or go the homemade posi-lok route for $50-$75. Not a deal breaker IMHO...
93 YJ, 4.0, 4.5" suspension, 33x13.5 Pitbull Rockers, Custom scratch and dent job...
05 WK, 5.7 Hemi, Quadra-Drive II