I searched the forums and didn't see any threads about the older models, just the newer ones, so I'll add this.
On my '93 I had a popping sound coming from my front end when I slowed down, followed by both fork seals letting go. Not a big wheelie rider or ditch jumper so I wondered why.
Upon inspection, my bushings measured 0.033" thick. Stockers are .040."
Unfortunately, mother Kaw threw us owners of the older ZGs under the bus along with 1300cc Voyager owners--they obsoleted the outer bushing.
Lucky for us, Racetech still makes bushings for our bikes! The part number for the obsoleted outer bushing is FMBO 41122 P. It costs double the price from Kawasaki but at least it's available.
Here's the Racetech page:
http://racetech.com/ProductSearch/2/Kawasaki/ZG1000%20Concours/1986-93After the bushings were installed, the problem cleared up for the most part--still pops sometimes though.
I'm betting that the sliders are worn out.
So, when I lose another .1mm on my discs (they're at 4.6mm right now) a front end swap is going to make a lot more sense if I still have the bike.