Well I got one of these new fangled Chevys(1988) that only needs sparkplugs after 100,000 miles. So after I replaced them in 2002, I figured I was good for another 14 years. Sure enougth, just seven years and 34,000 miles later, the truck starts running rough. I'm thinking it can't possibly be the spark plugs since I just replaced em a few years back, so I brought it by my more mechanicly experienced freinds house for a listen. He checked the exhaust temperature at the different cylinders with an infrared device, and noted that the exhaust leaked so bad it was hard to hear much of anything. After I explained that there wasn't much point is fixing the leaks since it passed the anual inspection in spite of them, he suggested that most engines run better with new plugs in spite of what Government Motors claimed. I decided to replace the plugs, and since I'd have one end of the wire off, I'd replace the wires for good measure, and since the wires were off the cap, it wouldn't be much more work to replace the cap and seeing that the cap was off anyhow, I figured on replaceing the rotor too. Well, all those parts were so cheap at the store, I picked up some new oil and a filter and since I was doing all this preventitive type maintainence, I aquired a new air cleaner and a p.c.v. valve to boot. I kind of hated to waste the good oil that was in the crankcase, but even if it wasn't worn out yet, it was still pretty dirty after 34,000 miles, and a new oil filter is always a good thing. While I was at the parts store, I noticed I still had some checks left in my checkbook, so I bought an upper radiator hose too. The left bank of plugs came out fine, and all but one were in good shape. Happily noting that I had most likely cured the problem, I proceeded to the right bank. The first plug broke right off, but I was able to remove the remainders with a large easy out. The second plug was more cooperative, but the third one snapped, and left a good portion of insulator in the head. Needle nose pliars and the easy out resolved that situation, bringing me to the moral of the story, if you live near saltwater, alternate the direction in which you park, elsewise your spark plugs will not rust evenly.