You may have to screw the cable back onto it & use that to wiggle/pull the assembly out. If they haven't ever been out they can be fairly stuck. It's a tight fit, with only an o-ring to seal it. DO NOT PRY ON THE TAB
A word of caution - when you re-install it, MAKE SURE IT IS SEATED FLAT! That tab is very prone to breaking off, and tightening down the bolt when it's not seated all the way will snap it right off. If this happens you can make an improvised bracket to hold the assembly down, it doesn't see a lot of force.