Its still an 800CC 2 stroke engine, top ends should be freshened up once every 2 seasons (depending how much you ride). Make sure the engine warms up properly before getting into the throttle. Also make sure the carbs are jetted properly and there are no cracks in the intake boots.
The pre-800 ho motors had flaking ring problems. It was never an issue , except loss of compression.. I believe they had mid 130 HP If you could find a 2003, you would be much better off. It had the 800HO, RER, better seat, risers etc...
Mine was awesome but nothing lasts forever. Mine went 7800 kms before i sold it in premium condition. It had 3 sets of pistons and a new crank and new boots and two thermostats. All done as preventative maintenance. Actually the last set of pistons was because of a cold seize. ALWAYS WARM IT UP! Also always use premium fuel. The manual will say regular but gas is different these days.
Just when you buy it budget for new pistons right off the bat. Its easy to do. Those zx ones are super easy go work on.