I'm guessing this is a 5spd, so it has a viscous coupler. The two things that the car will exhibit if it is failing, is a tendency to hop or bind when the steering is at full lock (think low speed, parking maneuvers) The other is a whining, space ship-like noise on accelerating indicating the bearings in the transfer case (specifically the coupler, most of the time) are bad.
Other than that, there is no reason to cite a center diff. issue. The first necessitates a new coupler, figure on $375-400 for the part, 3.5 (shop time) hours to replace. The second is about $45 for bearings, same labor.
Transfer case repairs are really not that hard, since the trans stays in the car, just the exhaust and driveshaft have to be removed (oh and the shift shaft) It is a good time to replace the associated seals, while you're in there.
The description you gave of the tech's diagnoses, sound like it was done on a lift (wheels in the air) Have you driven the car ??