Help me make 250,000

I have a 93 corsica with 235,000 miles on it. It's a 2.2 L 4cyl, auto with a problem in the rain. Driving through a thunderstorm a few weeks ago, it suddenly started sounding like it had fuel or electrical issues. I put a couple bottles of injector cleaner in the tank, changed the oil, spark plugs and wires, and it seemed to help somewhat. It stuttered when idlling a bit, but ran smoothlly once I hit the gas. Hitting another thunderstorm a couple of days ago on the interstate, the problem reappeared, only this time, even at highway speeds, it won't clear up. I tried replacing the fuel filter, but it's rusted on. The interesting thing is that, while the engine is running, I can remove the number 4 plug wire and the rough idling stays the same, while removing any of the other 3 wires results is heavy chugging. Since the plugs and wires are all new, should I consider replacing the distributor? Would driving through rain affect the distributor? Thanks in advance.