Does the new seal appear to be too small in internal diamater? Have you taken off the chrome collar around the group? (held on with 3 bolts).
Once you take it off you can clearly see the brass group that the seal slides over. On mine it was a snug fit but I could fit it with firm finger pressure.
I ordered the conical seal (as the old was conical), coffeeparts item 700623, but the normal flat seal is also available (700149), with the same ID/OD. I also bought the spacer (700200) but have not used it, as the handle locks in at 90 degrees.
This page shows the group on my machine: