Those were the instructions I followed. This is the step that I had trouble with (or rather the step after putting the o-ring on):
http://faq.ninja250.org/wiki/File:4Winterize.jpg
I had a hell of a time trying to force it through back through the plate while people on Youtube were able to pop it on with ease. (
https://www.youtube.com/watch?v=otJlx493OXE#t=339 - at 5:40)