How important is the rubber o-ring on the dust cap of my Crank Brothers Candy SL pedals?

One of my pedals was squeaking quite a bit, so I pulled the dust cap and lubed the spindles. When reinstalling the dust cap (it's a threaded cap), the o-ring in the threads repeatedly popped out - even when it would stay on the threads while screwing in, it would catch and eventually part of the o-ring would crimp and stick out. The dust cap is in tightly but the oring has a little bit sticking out.

I'm wondering if this is an extremely important piece or if I can get away without it for a bit? I figure I need it, but was trying to avoid paying $15/pedal for the rebuild kits just to get this darn o-ring.