Last night I got the car up on stands in the garage to look at the gearbox fluid level. Part of the objective was to decide if I felt I could tackle removing the gearbox myself if it comes to it. It has to be in the garage because 1. I have to work on it in short bursts over a long time and want to be able to close the door and walk away and 2. Winter is on the way - I have a full plasterboard roof in the garage so it's easy to keep warm! 3. I just don't enjoy working on cars outside anymore. I like the privacy of the garage, doesn't disturb the neighbors and I can listen to music etc while I work. It's decent size single garage but the A6 is a big car and it's fairly tight. I have done plenty of work in there without problem on this car, but gearbox pull on a car like this is going to push the limits of available space.
Enough space to work on each side, but tight:
Not much space left at the front. Plenty to work on the engine but certainly the gearbox would have to comes out the side:
The other option would be go in backwards, allowing the door to opened to create more space at the front. Or slide the box out the rear. Going in backwards would allow a crane to go in easier, which may well be needed.
Before lifting the car got the spirit level out on a few points so that I could ensure the car was still level when lifted, which is essential for the fluid level check:
Originally the car had a leak at the transfer box output seal so it had been covered in oil. That had all gone but I could see what appears to be a very small leak of ATF where the box joins the engine:
Therefore, it may well be that the fluid level is not correct, even more important to check it.
I think I found the fill plug which is hidden behind this lip as in the picture:
That's a really awkward place to get to, especially because you have to watch for a steady drip of oil to know when the level is correct. With it in this location, it's almost impossible to see, so I wasn't sure if I had the right plug. When I did a fluid change on the HP19 box in my other A6 tdi, it was much easier as it's all done through the drain plug.
Looking at the feasibility of pulling the box myself, it certainly looks like a serious challenge. Exhaust would have to be split as clearance is minimal. I do not have the standard exhaust system so I'm not sure if all cars are like this:
One of the worst bits would no doubt be getting the downpipes disconnected from the headers, as the bolts do not look in good condition and may well need cutting off, and almost totally inaccessible on one side:
The good news is that it looks as though removing the subframe completely would give a lot of access and really open the area up, so I guess that's essential for removing the box.
I can see various connectors and shifter cable, but otherwise it looks like a case of:
1. Remove Subframe (not sure best method)
2. Remove exhaust downpipes/mid section
3. Disconnect everything on the box
4. Unbolt driveshafts and prop shaft, secure out the way
5. Unbolt the box, which will need to move back slightly and then down. To do this I would be looking at purchasing a floor transmission jack on rollers - at 140KG it's just to heavy for messing around with. I don't know if a crane from above to give some support is essential or not.
I also realised that - I would need to invest in a better jack - to get plenty of height, and doing this job on 4 axle stands would be very hazardous! I would probably look at stands at the front and raiser blocks for the rear wheels combined with secondary axle stands. Wiggling a 140KG box around on 4 stands on a 2 ton car on your own is not a great idea.
So feasible? Probably, just.
Unfortunately I ran out of time to actually do the fluid change on the box so may look at this tonight or tomorrow...
I bought a single mass flywheel conversion, long story short, it was c###. If you can get the car up nice and high then I'd say just remove the gearbox. Once you remove the gearbox support brace you should have more room to remove the downpipes. 
