As with the La Pavoni, if the right grind & dose are used, not much force is needed. That's how the ES3 lever can remain a slender design. You would hurt that ES3 part if you consistently ground too fine and pressed/pulled hard for instance. In my use of the machine I found that the best tasting extractions come when you can regulate the flow by pressing a little harder or less hard. Not when you need max pressure to get any decent flow at all.
The seals are all available from Strietman.