Just loose ball bearings inside, so easily replaceable. If you're not super fussed about keeping or using the original plastic endcaps, then get in touch with Fuzzynod on here. He can supply you with an aluminium replacement. It's a 'pignose' style that just screws straight in. They look cool as you like, I run them in my DX slightly protruding from the pedal cage which gives excellent protection (i'm still riding mine).
Otherwise, good luck in finding new ones.....