Finally got INPA up and running today, using a OneStopElectronics KK USB adapter. Had to update the daten on the copy on INPA I had downloaded, in order to get INPA (EDIABAS actually) talking to the DDE (DDE 5.0 for M57TU).
Checked for errors and got four minor codes (all recent by the distance recorder):
4212 Gluehkerze Zylinder 1
4252 Gluehkerze Zylinder 5
41F1 Elektroluefter
4B22 Elektroluefter
The first two are related to glow-plug activation - (Glow Plug Cyl x - Activation Interrupted) and the last two are aux. fan related (41F1 Electric Ventilator - Short Circuit to B- & 4B22 Electro Ventilator).
I'm guessing the glow-plug "errors" might be a timing thing - how long I wait before starting the car after turning on the ignition. I DO see the "Pre-Heating" message on really cold days - comes on for 3-5seconds - but these errors are logged on warm days when the glow-plugs shouldn't be called up. Dunno...? 
Car starts instantly, summer or winter, hot or cold.
The aux. fan codes are going to cause me lost sleep until I pull the unit and check for corrosion in the central housing - the fan runs fine but something is causing the errors. I'll run some activation tests with INPA on the weekend to confirm this.
INPA - a whole new world of worry! 