It is leak tight and all the oil scent in the cabin is completely gone.
However I'm not going to leave it as is.
The rubber is soft (obviously) and the layer is too thick, so too much material is squashed out of the mating surfaces.
On the outside this is not a problem, but you don't want to reduce the pipe diameter as this might kill the turbo due to oil starvation.
This is also the reason why you should not use RTV on the mating surfaces. You never know how much ends up in the pipe, reducing the flow there. As it is not pressurized you don't need much blockage to disturb the flow...
That said, I'll cut another seal but now out of 0.3 mm sheet and see what I'll end up with.
By the way, Google showed a lot of results on warped mating surfaces of turbo oil return pipes. Also my friendly Porsche 911 turbo neighbour immediately said "warped turbo mating surface' without me telling him anything else that there is a leak i can't fix...
In the process i replaced the hex. bolts for allen key's for better access from below. If you use an extended Allen key in a socket, removing the pipe is a piece of cake now.
To be continued...