So replaced spark plugs (not going to show you how crap the old ones looked - very fouled up). Did not go one step colder - unless you tracking the car I don't think its worth it.
Also did injectors - not changed since new, so the 20yo injectors were swapped out for OEM new.
Added new AIT sensor as the ears on mine had come off.

I think I still have a vacuum leak somewhere so will want to chase that down as I still get the occasional load limit P1999 code and exhaust chop on low rpm overrun. Any thoughts on where to start looking on the vacuum leak side?

Replaced my Kleemann TCU that I got for the 2.82 diff back in 2010 or there abouts. Much better tune and car shifts quite a bit smoother (pretty quick in M [def quicker than before]. It also has an "A " mode or Active mode which I still need to get my head around but it targets a gear and tranny shifts optimally around this gear point - dunno will need to test. If you want a link to this supplier let me know or ping him directly i Germany at tcutune@gmail.com - He was also a sponsor on the M539 UTube channel where Streten was refurbing an E55 wagon.

Anyhow - she is running pretty well and the Tune Up definitely been worth it. Just to find and sort the vacuum leak now.

Use brake cleaner and spray around the areas you think are leaking and see if the idle changes. Most use carb cleaner but that stuff is really flammable when engine is hot so be careful with that.
If you have a smoke machine even better.