depends on how they're put together ime..

some have the bolts and use a rubber o-ring to seal it.. (these seem to be easier to split to me).

others just have the 3 pieces and people use (often lots of) RTV sealant to seal them together.

Currently I'm having major hassle trying to separate my last one. (i've got the outer off but the centre and the inner rim just will NOT come apart), so if anyone has any great tips please pass them on! I've tried using stanley (which worked fine for the other 3), tried silicon eating stuff form B&Q (didn't even rtouch the sealant, just discoloured the rim where it came into contact, but luckily that won't be visible) and am now at a total loss. Don't want to hammer a screwdriver or similar in the split them as i guess this would ruin the actual rim!