Hi guys I am new to this to please forgive any errors etc.

I have just bought a 1999 A3 1.8 Tsport quattro the radio has what seems to be a well known fault with the volume control and I am considering changing the unit but want to try and keep the car as original as possible. I have found a concert plus for sale and believe this is the model that has the volume issue resolved. Can any one confirm this please? Also the one I have found is from an A6 of a similar age will this fit my A3 as a straight swap?
Thanks in advance for any advice.