Those plastic cups/retaining rings are really fragile and the only way to protect them is to remove the drive-side cartridge first. I broke a couple finding this out the hard way too.

If you buy a new bb, it will come with the metal NDS ring and you can use that one indefinitely so it will be there when the current bb dies. Unless you can find another LBS with a left-over metal ring from someone else's trashed bb, that's the only way I know to get one.