Re. the UE900: I didn't realize that they retuned them. I had a pair in the past and thought they were a bit dry and mid-centric, but you've just piqued my interest to know more. I'll have to check that thread and do my research.
Re. the C5: I find that they sound really bassy, maybe too much so, when I use the stock tips and jam get a proper seal. If I pull them out a touch and break the seal, it starts to lean toward the sound I’m looking for. BUT, I loose all isolation, and living and commuting in NYC, that’s a necessity. I put an order in for various different tips and will see what I have at home to experiment with.
Re. the P7: I wonder if the looser seal can be achieved by softening the leather pads. I remember them being a bit stiff when new – definitely stiffer than how they are now. When I first got mine, I also remember wearing them a bit lower on my ears in order to create a gap around the back of my jaw. That helped. I don’t have to do that anymore, and I wonder if it’s because of what I mentioned about breaking in the pads.
Re. the W40: Truthfully, I didn’t think much of it at the time, but I did see a larger seam at the top of the left earphone. It wasn’t a full split as I saw in some of the photos floating around and now I’m wondering how that would have held up if I kept them. Have you tried contacting Westone about it or returning them to the store?