The coil packs probably need replacing occasionally on these anyway. If the old one is still servicable (not swelling or clear rust visible where the plastic gets hairline cracks, keep as a spare, and acquire some replacement boots.
Over the years, I have found the biggest killer of the coil packs fitted to the 2.6 / 3.2 is water ingress into the plug wells which accelerates internal corrosion, which can be seen on the metal core at each coil upper end (thick end of the rubber insulator boots), and rusty cracks. Oil in the plug wells will cause the insulator boots to perish at the plug end.
But taking these two causes out of the equation, coil packs should last for an infinite number of years. I have only had to change them on other cars as a result of another issues causing the problem, ie water leaks from the scuttle or oil from the cam covers.
I have a 2.6 that is still on its original coil packs, and it is now approaching 19 years old and 70k.
Probably jinxed it now....