Thanks for all the replies. I went ahead and bought a few o-rings and I'm going to change it out, since I need to change oil soon, anyway. I tried to tighten the adapter but it's as snug as I can get it.
I'll report back with the results.
Yes, it is the Kawasaki. FR691V
Model number is 17RIEACZ010.
That was my suspicion, the o-ring was bad. Just started noticing it recently but it only leaked every so often.
I've found small leaks of oil on the garage floor but couldn't tell where it was coming from on my ZT1. I cleaned the frame and laid a paper towel under where the drain valve connects to the engine and that does indeed seem to be the culprit area. Could this be a bad seal?