While the maximum pressure on the seal is 88 psi, that is only in the corner. On the side, the pressure drops to about 70 psi (light orange color). The seal fails when the lowest value around the perimeter fails. There is a natural split line on the geometry, so simply choose all the faces above that to apply a pressure.
Under analysis settings, make this a 2 step solution. In step 1, the pressure is 0 and the displacement of the center part ramps up to 5 mm in 1 second. In Step 2, the displacement stays at 5 mm and the pressure ramps up from 0 to 100 psi in 1 second.
I followed my own instructions and was interested to learn that the pressure actually helps the seal work better! Below is the pressure at 76 psi (time = 1.76) and you can see the peak contact pressure is now 170 psi because the pressure is pushing down on the top of the seal, which causes it to compress against the bottom and expand sideways making the contact pressure increase.