I think the seal is OK, because the bass is strong and good. Stock tips are really not that good, I use now the IE8s foam tips, which give a slightly better result. The silicon tips of the IE8s don't fit well.
It seems that I'm not the only one with this problem, although most people are satisfied, there are some comments here about similar opinions of its treble.
I'll wait a few more weeks, and see is further burn in helps, but don't have high hopes. It seems that I can get new replacement driver for my IE8. If its not that expensive, I'll replace the bad left side and use it for a few more years. I think I was just hoping more after the positive reviews, and reading such things, that its similar to the M50. No, it is not, they are sounding completely different.