What has been done to it as far as maintenance goes?
In general, there are things that need attention annually and some that can be done every couple of years depending on usage hours and usage conditions.
In addition to the typical items like gas filters and separators, lower unit pressure checks and oil drain and fills Optis require frequent checking and possible replacement of the air compressor air filter, the water screen inlet tube for the compressor cooling water. If either of those items gets blocked you can cause serious damage. The spark plugs if Iridium ( and they should be) can last a while , but they should be checked if never done.
There are linkage adjustments that should be checked as well as the adjustment of the throttle and shift control cables.
Opti thermostats and poppet valves are common maintenance items.
Note that on earlier Optis, some plugs and the compressor water pickup are hard to get to and most likely will require removal of the lower cowl ( a knuckle scraping task on early Optis).
A tech should query the ECU for faults and address accordingly especially if the motor has generated alarms.
Of course there are other things that can be checked like fuel rail pressure, tracker valve operation and injector performance.
There are many things on optis that can act up, I tried to list the more common ones.
