When you say leak... do you mean from where it connects to the atomizer or leaking into your mouth when you inhale?
I have a DSE901 and have yet to have a problem with leaking at the connecting point. However, I have had some problems with leaking into my mouth (ick). My recommendation for that would be to fill the cart less, then the problem seems to go away.
If it's leaking at the connection point, I have seem a few solutions on the forum. Using a small film of glue on the dura cart to make it a bit thicker, cutting scores into the connecting point on the cart. I haven't read of anyone trying a small layer of electrical tape, but I think that would work too.