Have a rigger replace the grommets. Older containers may have brass grommets. Brass grommets wear out. Pins can dig grooves into brass grommets. Pull forces will increase because of the increase in contact surface area between the pin and grommet.
Grooves can inhibit lateral movement of the pin as it's being pulled, that can increase pull forces.
Brass grommets corrode too. Corrosion can dramatically increase pull forces, especially if the pin hasn't been moved recently. Discoloration of the brass is a sign of corrosion. Older containers had brass grommets installed everywhere. Any brass grommet located on the top flap of either the main or reserve container should be replaced with stainless steel grommets.