I blew the o-ring out of my dominator pump and replaced it with a new one.  It seems to have a lot of play back and forth with the new one on.  Is there supposed to be a lot of play??  Seems like there should be some kind of seal with a new o-ring???  I first bought a large size o-ring that didn't fit the grooves.  The smaller size o-ring fits the grooves but now there is a lot of play...

Any help appreciated...