Yeah you should have the engine disassembled and cleaned very well and closely examine all of the gears
and check to see if the gear dogs and slots are rounded and all of the other parts too.
and if you need a total engine overhaul like a full tranny , crank rebuild , cyl plating , piston, clutch baskets and plates,
gaskets, and if you get it done by a shop then you are looking at around $2200 parts included++ .. well at least thats how much i paid for my engine and thats not including the other costs like the plastics , paint, shifters and kick start, bearings , fork seals and so on.
if you are looking for a part that is not available (as most parts are not from kawasaki) let me know what it is and ill try to look for it for you.
i do have some decent parts i am willing to sell. i have a decent clutch basket, hub and plate. and 20 new oem spokes