JVM - I'm not certain what your issue is; one of the techs needs to chime in to provide more input.
I find the following for your code: P1 747 Electronic Gear Selector Module: Defective Interaction of CAN with control unit A1(instrument cluster)......that might play into your other dash instrument issues too. Does the W140 have an OVP or K40 relay like the W210 suppying power to those devices???
You should NOT have fluid at the harness connector. You need to check the opposite end where it connects to the ECU as fluid contamination wicking up the cable can fry the computer. It should not leak when replaced.
The dark fluid is not necessarirly bad; mine was brownish and smelled like 80/90wt gear oil when I changed it.
http://www.peachparts.com/shopforum/showpost.php?p=702285&postcount=8 Sounds like it is overdue for a fluid and filter change at the least. MB fluid only. Use fluid for the 722.6 or newer 722.9 only. No equal. Will need the factory dip stick tool (dimensions posted on this site if you want to make your own) to check fill level when at 80C; the sealed trans dip stick tube is empty.