On the topic of find the cause of the problem instead of throwing parts at the situation I completely agree, but I can't help but remember getting to the end of my wits [and telephone book sized Honda factory service manual] when I was faced with the prospect of replacing the ECM in my 92 Accord at only 75,000km. After all the testing for an intermittent fault, the manual stated: "Substitute known good one" which at the time was $800.00 I called Honda and asked the parts guy how many of these things fail? He said not very many.
I got lucky after I think the third time removing the horizontally positioned distributor cap and found a small piece of porous metal laying inside. Turned out to be a failing distributor bearing resulting in one of the three rotors making contact with the pick-up coil. It wasn't skill, it wasn't expertise, it wasn't following the manual, it wasn't the process of elimination. That little piece could have just as easily dropped on the ground. Luck I tell you, sometimes you gotta have luck!