Time for an update. Thanks again to RedruM69 who tackled a new M5126 MB and got it recapped. Slipped it into my existing case last night and it worked right out of the gate. It did take some doing, but I now have a working M5126. I also have the parts of an "almost" working spare, including a German keyboard! If anyone ever solved for a replacement backlit screen cable please let me know.
This was one of the first projects I tackled. Since beginning on the Portable I've conquered (with tons of help from others) a couple of Lisas, Apple II/+/Plat/IIc, and a slew of 72xx. There is still a huge pile to get working, but so far so good.