While you have the actuator out you might as well check the bottom diaphragms. As you can see here, they are often in much better shape.

However, after removing the retaining rings, you'll probably find some dirt and grit hidden beneath. This can work under the edge and cause slow leaks, leading to overnight leak-down of the system.

Given this, consider pulling off even diaphragms that look good to give them a gentle cleaning.

Re-install and grease the diaphragms as well, and then clip the retaining rings back in place.