All the advice you are getting here reflects my experiences as well. I'm the owner with the current engine electronics gremlin. On your list of work done, the LH control unit that was replaced is part of the electronic engine management, and the rear axle speed sensor is related. I'm not a mechanic. My car has been in and out of the shop trying to fix this problem since November. Spent about 3k on that so far. Before that happened, I was using it as a daily driver.
The other thing I would check, if you buy the car, is the driveshaft flex discs. Regarding the new trans and diff, leaking seals might have been caused by driveshaft vibration. I'd suspect the flex discs and I would look real close for evidence of front end or rear end body damage.
1995 E320 Wagon Moonstone Grey/Parchment 106K mi.
2007 E63 AMG Graphite/designo 75K mi