Are we talking about the plastic cover for the raceface bearings? Cause those are indeed pretty easy to mess up. Once they pop out they are a pain to get back in without cracking them. Mine is cracked a little on the inside sleive, but since that part is very tightly sandwiched between the bearing and the axel I see no potential water entry point. If the outside face is cracked too, raceface can probably send you one, although installation is always a hassle.

Maybe there's a tool or method for this somewhere, since although you're not supposed to replace your own bearings, I'm sure people will eventually do it anyways.