It's a shame Sennheiser have discontinued the IE 400 Pro's. So grab them whilst you can. I'm not sure what they have succeeded them with either.
I wanted to get a replacement right earpiece, as mine fell apart months ago when I changed the tips. I must have pulled it wrong, and the capsule came out of the shell. While I managed to glue it back together, I didn't align it quite right, and it's never felt the same.
Individual replacements were available previously, but I finally got around to ordering one this week, but it seems you can't get them anymore.