I finally found the time (and the courage) to check on the two possible solutions to my check engine light problems. I used to do all the work on my cars when I was in high school and college and had no money, but I've gotten kind of lazy over the years...
The #5 fault code is an EGR valve problem. I had already replaced this, but since the code came up again, I was blaming the light on the wiring harness, but this had already been replaced. Since I had nothing else to blame on this problem I knew I had to find a solution, expecially since I've thrown about $2,000 at this problem.
Thanks to Arthur Dalton's suggestions, I checked out Steve's article, and he commented on a similar problem on a C280. The problem was the hot pipe inlet to the intake manifold was carboned up from PCV (partial crankcase ventilation) vapors. To test, I applied vacum at idle, and the engine idled perfectly, suggesting the port is plugged up. This test took about 30 seconds to perform. I can't believe both the dealer and two independent mechanics missed this.
Regarding the #26 code, I located the shift delay valve next to the master cylinder. It has a black plug with a green wire and black wire leading away from it. I pulled off the green line, blew in and out on it, and sure enough, it is plugged. I dropped off the car at my mechanics last night who charged me a good deal of money to fix the car, and didn't. Needless to say, he's performing this for free! After all, I explained to him that he should be paying me as a consultant for his ongoing education.