I used this guide to start, but had to change things around to work with the C5 chassis: https://forums.quattroworld.com/s4s6/msgs/231631.phtml
The front bushings for the allroad (4Z7505145D) seem to be relatively rare, and sell for $100+, EACH. However, as best I can tell only difference between the allroad subframe bushings and the regular A6 subframe bushings are that the allroad bushings have 2 holes drilled in them to allow them to mate up against the subframe spacers with metal dowels. I ended up buying the regular A6 bushings (8E0505145L) from FCP Euro for $8, and drilled 2 holes myself.
Jack up the rear end and put it on jack stands
I put the jack under rear diff carrier and put jack stands on either side on the pinch welds. Keeping the car level is important so the subframe doesn't have any sideways movement or pressure.
Remove the rear wheel, and remove T25 screws from the wheel well liner
You don't need to remove the entire liner, but enough to peel it back and expose the front subframe bushings. Keep track of which T25 screws came from where - there are 3 different lengths depending on where in the liner they were removed from.
Remove the subframe mounting bolt
Using an 18mm socket, remove the long M12 bolt holding up the subframe. Once this is removed, the subframe will drop slightly. I did not need to remove any wires or brake lines.
Make a note of the mounting orientation for the bushing
Take a picture if you have to. The hole in the center is oval and offset. You will want the new bushing to be mounted as close to the same way as possible.
Cut off the top of the old bushing
Using a sawzall and a metal cutting blade (I used a Milwaukee Torch), cut the top of the bushing off right up against the subframe. Be careful not to cut into the subframe itself. This was relatively quick and only took me about 30 seconds to cut through the entire bushing. Once the bushing has been cut through and removed, cut through any remaining rubber that is mushrooming above the subframe. I used a flathead to pry the rubber up and a razor blade to cut it off.
Pry the metal plate off the bottom of the bushing
Using a chisel or flathead, hammer between the metal mounting plate at the very bottom of the bushing, and pry it off. This should peel off fairly easy, as it looks like it is only barely glued on.
Drill through the rubber bushing from below and cut out the center
Using a 3/8" drill bit or larger, drill a hole through the bushing from the bottom. I ended up drilling 4 holes. I then used a jigsaw to cut around the bushing from below. It doesn't need to be completely cut out, but get as much as you can.
Pry out the center of the bushing
From the top, I used a crowbar and was able to pry the center of the bushing down and out. My first attempt I did not cut enough of the rubber out with the jigsaw, so I had to go back and cut more out several times.
Chisel the outer sleeve from the subframe
Using a chisel or flathead, stick it in between the plastic sleeve of the bushing and the subframe. I started hammering parallel to the ground, and slowly turned the chisel vertical. Once I got the chisel completely between the sleeve and subframe vertically, I was able to pry out the sleeve.
Clean the subframe surface
The top and bottom of my subframe was pretty corroded, and sat proud of the internal ring where the bushing needed to go. I used a file and wire brush to clean it up, then added a small amount of high temp grease to the bottom lip to make it slightly easier to install the new bushing.
If using a regular A6 bushing, drill the mating holes
From the top of the bushing you previously cut out, separate the subframe spacer from the old bushing. There will be 2 metal dowels connecting them. If either one is still in the old bushing, pry it out with some pliers and hammer it into the spacer. Using the old subframe bushing as a guide, drill 2 holes in your A6 bushing. I ended up drilling 2 holes with a 11/64 bit, which allowed a perfect fit for the dowels. Test fit the spacer and new bushing, and make sure it can mate with ease - you will be fitting these back together blind.
Press the new bushing into the subframe with a floor jack
Here's where things got creative. Did I say creative? I mean sketchy.
The front bushings on the subframe are mounted at a ~10° angle. Using a floor jack to press in the bushing straight up isn't really feasible, because it would just press the bushing in sideways, kink it, and break the bushing sleeve (can you guess what I did the first time?). What I came up with was to use 2 rhino ramps under a floor jack, which gave me the perfect angle to press the bushing straight into place. This could easily be recreated with a few 2x4s if you don't have ramps.
Using the bottom metal plate from the old bushing, I taped the largest socket that I had to it, upside down. I then set the metal plate on top of the hole for the subframe bushing, with the socket facing up towards the car. This prevents the subframe from bending too much and changing angle as the new bushing starts to get seated.
With the jack resting at an angle on the ramps, and the bushing oriented approximately the same direction as the original (you did make sure to note the original's orientation, right?), I started pressing the bushing into place. I did this very slowly, and if the bushing started tilting too much to one side, I backed off, readjusted, and started again. Eventually, I got the top of the bushing fully insert, and the sleeve was just starting to push into the subframe. At this point, I removed the metal plate from the top of the subframe (since it would prevent the bushing from popping through the other side), and continued to jack the bushing into place.
Reattach the subframe spacer
From below, I looked through the hole in the bushing and lined up the subframe spacer until I felt the 2 firmly mate with the metal dowels. You won't be able to see where the mating holes are, and will have to slide it around until it pops in place.
Reinstall the subframe bolt
The subframe bolt is supposed to be a TTY (torque to yield), so it should only be used once. Using the advice of 034 from a different car (but same size bolt, M12x1.5), I reinstalled the original bolt with blue loctite and 120Nm/89ft-lb.
Reattach the wheel well liner, reinstall wheel
Hopefully you know how to do this.
The first side I did this on took me close to 5 hours as I was trying many different things to get the old bushing out. I did the second side in less than 30 minutes.
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