I know you have had this car discussed on other threads but I just don't remember all the details. The problem as you have just discussed sounds minor. Diagnosis of such a problem in my shop would cost less than $150. Diagnostics and repair only get to the figures you state if one uses parts swapping for diagnostic technique.
We had a 300e in for a no-start last week. One of my oldest techs hooked up to the fuel distributor to watch differential pressure as he was sure the problem was fuel related and the electronics looked good upon testing. He brought me over and showed me that he had zero differential pressure (lower chamber pressure subtracted from upper chamber pressure). Within the next hour or more we tried a new fuel distributor and a new EHA to no effect. The tech was at a loss and I came over to help.
We use two different gauges to get the two readings (unlike the MB book way of getting both readings from one gauge and subtracting). After changing the EHA I decided that I wanted to see if the very small pressure difference between the gauges (no two gauges read exactly the same) corresponded to the appropriate way the pressures should be (one higher than the other). As I followed the lines I realized that he had both gauges hooked to the upper chamber; thus all of our testing was based upon a false conclusion. A couple more minutes of testing produced the real problem: a bad coil.
I mention all this because all testing is based upon hypothesis. Bad testing results in bad hypothesis and no solution. Every wire you looked at had a function. Every wire can be functionally tested. Efficient diagnosis is based upon finding whats missing and hypothesizing on a practical cause that then will be tested. Without direction, one just travels in circles.
Bosch Master, ASE Master, L1
33 years MB technician