2001 Audi A6 C5 2.7t - ABS Module and Master Cylinder Replacement

[Bagi]

2001 Audi A6 C5 2.7t - ABS Module and Master Cylinder Replacement -

My brakes locked up, all four and after bringing it to a mechanic this is what he wrote on the description: "Attempt to flush brake fluid, system contaminated, need to replace A.B.S. Unit and Master Cylinder and flush lines."

Brake fluid came out black from only the Right rear wheel, all other sides nothing came out. I bought the car in this condition and the car has a history of sitting/ not in use for several years. It had 99,000 miles when I bought it in mid 2019 and sat for most of 2020.

A new ABS unit from Audi is $2000 and I am not looking to buy a new one, I will be tracking down a used one but I need to make sure it is functional and it will work, preferably a refurbished one.
Part Number: 8E061102T

Does anyone know a good source to find a part like this ? with some level of reliability?

Also

Does anyone have experience with this repair and can give me any advice as to how I can go about it using used parts?

[Jawsman2]

I'll see if I can get a photo of the company tag that refurbished my ABS unit.