18k?
It's barely broken in
Seriously... that is low mileage. Things to start looking for are clutch slippage and loose timing chains. The timing chains can be easily fixed in an hour or two with a set of Chuckster's extenders.
The clutch is a little different... there are a couple of solutions. The system that I just installed results in a very heavy clutch pull that may be too much for those with a weaker grip.
Gadget's Fixit Page For Kawasaki Nomad & Classic Modification Maintenance & Repair
A lot of this is specific to the 1500, but the 1600 is very similar... identical in many aspects.
I've got 34k on my '06 and it's been a great bike. I'd buy another one in a heartbeat.