Mine was gone when I got the bike( upper valve cover chain guide rubber piece) my dealer had one shopped in so kawasaki still has them as of 2016.
I just pushed mine on to the two posts real hard with my thumb till it bottomed out to the valve cover.
I asked this same question when I installed mine and I got anything from glue/epoxy to just push it on there.
The manual doesn't say anything about sealants or glues so I just pushed it on.
Year later after starts and running the engine, it's still there. Soooooo.....in theory you could just put it on there, but if you wanted insurance, glue it.........