I am very very amazed by the work you have done and its impressive !! Currently my A6 is experiencing fault code P0851 with P1724, other than having some jerks during hard acceleration, the car drive without any issue. Wonder if you can lend in some thoughts in this.. Appreciate..

 

I no longer have my Audi A6 sold it and bought a 2007 E63 Mercedes. Don't worry that comes with its own problems as well. Your codes relate to the neutral indication and relay control for that on the transmission. So I imagine it could effect your ability to start the car at some point. Sounds like a worn switch or perhaps a dirty switch. Have you ever had anything spilled around the gear lever? If so you need to strip that all down and clean it carefully using some electrical spray cleaner. You don't want that gear indicator unit to fail they are not cheap.

 

No issue on starting the car actually, only thing EPC light up but car behave as normal. No spilling or whatsoever from internal as well, however from gearbox external, my driveshaft oil seals are leaking and oil residue has been all over the gearbox housing.. not sure if its because of that or this error is definitely pointing to the switch under the gear stick .. yes plan to strip the center console but labor cost charged by mechanic is quite high, so am buying time while saving enough for the job