Dreaded S5 gearbox fault?

Good afternoon all,

I currently own a very slow 2014 S5 coupe, bringing up the "Gearbox fault: You can continue driving, no reverse gear" message.
With an Audatex code scanner the only fault that won't clear is "P173D00 - Gear position distance sensor 4 implausible signal".
Googling around I can't find any information on this one code specifically, could anyone offer any advice on if this is the common fault, is it the mech unit and any extra info?

The fault came up once randomly so I pulled over and turned the car off and on again, it cleared. Few weeks later as the gearbox tried to go from 5th to 6th there was a grinding and then the revs shot up assuming it canceled the gear change to protect itself and since the fault has been permanently there every time I start the car, stuck in limp mode with the odd numbered gears and no reverse.

I have called a VAG specialist and they have said its a weeks work, gearbox out and all internals out for a minimum of £2500. However what I have seen online for the OB5 gearbox is new mechatronic units/circuits being fitted whilst keeping the box in for roughly £700ish doing it yourself, which fixes it. I am comfortable doing the work myself if this will fix it, but I want to be sure before doing so, so if anyone knows anything it would be greatly appreciated!

Thank you!