Have a similar issue - spent 2.5k with Audi to remove Engine and Gearbox removed and fit new Solenoid and various other parts. Car still failed to drive now I am told I need a new Gear Box. I have contacted independent Specialist’s to be told Audi won’t sell parts for this Gear Box to anyone other than Audi dealers.
My advice to anyone thinking of buying an Audi - unless you have a Audi Extended Warranty stay well clear