S4 B7 Tip Gearbox issues and potential replacement

Afternoon all from deepest darkest Bavaria,

Long time lurker here, have thoroughly enjoyed the posts over the last 7-8 years, thank you for the valuable information. Plenty of posts have helped me diagnose and rectify a whole litany of issues over the years.
The info here has helped support that complicated but special relationship I share with my black '05 Tip S4… One which I’m sure you all know so well. Indeed, we’ve been through all the usual long term relationship milestones most notably the full timing chain service 4 years ago.

To the issue at hand: Front cooler/radiator packs were damaged by a smallish front end accident, unfortunately the car was driven for some time after this.
Once the brown coolant was spotted and the car taken off the road - the whole engine cooling system and rads have all been washed/cleaned and replaced where necessary (ATF likes to swell rubber eh!). Finally the various rads and thermostats are all behaving themselves and the car heats/cools properly now.

On the first test drive however the gearbox still isn’t happy - the symptoms are that in 3rd gear and higher at cruising revs it feels like the valve body is constantly opening/closing the clutch packs, so the car surges and slows, surges and slows. Higher revs seem unaffected.

Gearbox oil has been changed 3 times, still some light evidence of milkyness. This time I’ve pulled the Valve body and am gearing up to tear the valvebody down and replace all the valves, middle plate, springs/balls, etc.
Hopefully this solves the issue, but I’m aware water damage may have occurred to the clutch packs so the main question for the gurus here:

If I bite the bullet and pull the whole box and source a replacement from ebay or similar. Currently I have 6HP19A HKF,

  1. I’ve seen JTR/HHU/HLB/HYL come up but I can’t get a clear answer, even from ZF what mine can be replaced with

  2. What coding, if any must be undertaken to the TCU to match it to the VIN/ECU, and who should I approach to do this for me (I understand VagCom can’t do this)

Thanks again you legends!