Steering is difficult only in winter ...

So... I'm just...
It's a strange phenomenon.
In the summer everything is ok ... In winter, when I have turned right, I can no longer steer back to the left.
But it's only on the first start when the car has stood for a while. After a while, everything will be fine.

I've written this thread before, I know... but despite oil changes there is no improvement in sight.

Are there any sieves or valves for the hydraulic oil that can be clogged?
The Audiwerkstatt is about to install a new steering transmission. And that's not in it right now.

Claudia