Hey all. New to forum and bikes. Worked on cars for a while but this is my first bike, 1990 ninja 500. Was going to change the oil and removed a plug (looks like a banjo bolt) from the right side of the engine (later discovered since minimal oil came out this wasn't the right plug).. Anyway when removed it was all cracked and seems to be good I found it because it is some sort of oil passage. It is left of the water pump and right of the oil level glass . looks like an m14 but is a very specific bolt. It is hollow in the middle and has a hole at the top for oil to pass tthru. It seals with an oring..

http://www.ex-500.com/wiki/images/5/5e/Coolant.drain.bolt.jpg

This is the only picture I can find its the lower left bolt in the picture. Thanks! (Not on the water pump)

 

You'll probably need to order it through a Kawasaki dealer or online.