I've lived with Zeta in it's hey-day for a few years. Now they go for about US 500.
Problematic area is sticking bearings. Adjust the counterweight so the arm is totally level, put anti-skate to zero, and move it from side to side and up and down. See if you can feel any catching. The arm tends to sound very dark, somewhat reserved, with huge bass. At the time it was the anti-pode of the Alphason, which is open, brighter but lighter sounding arm. Not sure how it competes with today's top arms, but in late 80's - early 90's it was considered just a notch below Fletcher's The Arm NC800, top arm in those days.