I have mine sitting in the box still because it has been too cold to install... Just took a look and it does have slits on both sides. Not sure what happened with yours but I'd get a replacement.
Yeah that's what I did. It was a bit of a pain to get it all clean on the ID and the burr filled down. I figure that would have made a good place for a leak if it wasn't nice and clean.
Too cold he says... I'm in Minnesota and I did it today. Now my car sounds bad as hell!! Just put on your carhart bibs and get it done.