Replacing one tyre on RWD axis?

[Andrei]

Hi all,

I just had all my tyres replaced early last year, so let’s say they are around 1y old tyres and used for around 12,000km. Recently I got a nail next to the side wall which is not repairable and need to replace one tyre on the rear axis.

The guy from Tyre shop said that I can replace only the affected tyre, as they have plenty of thread and the difference is minor. In the owner manual they only say “do not mix tires of remarkably different treadwear”. 
However, while researching on internet it seems that the opinions are split, some say to replace one if the ware difference is not more than 4mm, some say to replace both no matter what.

Did any of you had a similar experience and how did you resolve it? Did you replace both or just the damaged tyre? 
Thanks in advance for your help.

[bazzle]

Depends on how worn. You can prob go to about 3 to 5% difference on a non lsd axle.