Personally i'd replace due to the cost of it, and peace of mind, but if you know it's been done recently then maybe not....
Anyway, if you take off the distributor cap, rotor arm and the dust cover thing (if there is one), you should be able to see the sensor and the wires, often these corrode or degrade over time and cause a missfire. "Usually" if I may go out on a limb here, most missfres on these engines are caused by either bad crank or phase sensor, but can also be a mutitude of other things, pkus thiese are easy and good places to start your diagnosis.