Check the canister body itself. My 2213 came with a small crack in the canister body, so I had to get a new one. They aren't too bad though in terms of price, and can be had for around $10.
I could give that a try. Are the directions on http://www.atomicrice.com/atomic-o-ring-installation.pdf comparable to what you used to open up the top?Take the gasket out and apply a thin layer of vaseline. That worked for me on my 2128 pro II.
Don't use Vaseline. It is no good for the seals and will degrade them over time. EHEIM Lube is silicone based. I couldn't find it so I bought some stuff made for tap o-rings.
There's a quote of an email from EHEIM saying their o-rings are not silicone based and that they use silicone lube
I so just LOL'dI have an Eheim 2206 (pro) that recently confused itself with La Fontana di Trevi and began shooting water out of its side when I turned it on. Very artful, but bad for the rug.