Jim,
I thought there was a separate cable for the ETA - If he's had the MAF replaced, the condition of the MAF wiring would be fine. I think that just to be on the safe side, he should open the ETA cable and make sure - it won't cost him any money, and he then knows for sure, instead of having that nagging doubt in the back of his mind.
He needs to open up the lid and get a part number off that module too, and start shopping/hunting for one - brand new is cost prohibitive, unless one has cash to burn.
(yes, I have one for sale, but mine's for an ASR equip'd car)
PS: geez, with all these abbreviations, I hope I am understanding and typing everything correctly.
PPS: I just re-read the posts and it appears that the MAF is most likely the same age as the rest of the car. But, that doesn't necessarily exclude the ETA from having bad wiring - since the MAF was most likely bought from a company that didn't build their products with defective wiring the way Benz did. (yeah...another jab at MB and their cruddy harnesses)