That certainly looks plausible, though as it has 5 connectors I've probably missed one out above. :o
(Probably overlooked T3bl for the N110 locking solenoid)
If it's easy to extract and replace that's where I'd be heading. +++

Yes I believe so based on the wiring diagram. I have one on the bench as I was investigating earlier so I can have a closer look tomorrow. The 10-pin connector T10g is at the front of #26.

I suspect the TCU will be ignoring the steering wheel buttons in D since it has the F189 error.

Can you get the part number of your TCU from VCDS please? I have some 2002 S8 units but worth comparing numbers to be sure, although they are fairly interchangeable.

Should be relatively easy to test the diode with a multimeter if you can get the loom out.
It's between T5g pin 4 and T10g pin 6.

Thanks again.

I will check the TCU number tomorrow. Do you think it worth swapping the TCU over before extracting the shifter again to try and remove part #26?

I'll defer to MJ on that, but if she can loan you both TCU and loom that would be handy.....

Well, the TCU is easier to get to than the shifter so that's what I'd do first.

Looks like the TCU number is 4D 927 156 EC, with software version 1010 – does this sound right?

Yup. I should have one of those +++

That is great – and would you by chance have a spare loom (item #26) I could try too? Just let me know how you want to go about arranging the deposit etc – if the offer still stands!

For future searches, this was solved by swapping the TCU +++