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I will try to put some thin metal foil between seat post and frame (like some others already did to prevent slipping) in order to get a even gap on both sides in clamped condition and will report about the outcome.
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Finally found some minutes to elaborate on this topic!
in Short:
my saddle looked the same as for Siejak, - I was able to fix it by inserting three small sheets of a soda can metal foil at the right side between Seatpost and Frame. By doing so, the Saddle was perfectly aligned.
To those who are affected, - just loosen your seatpost clamp and try to rotate the saddle to the left and right. I was able to rotate it by approx. ± 5 degree. As soon as the clamping device is tensioned, the notch of the saddle rotates to the right and the gap between seatpost and frame looks like described in the prior post.
If someone is motivated to dig deeper: Maybe the root cause for the misalignment is not the huge clearance between seatpost and frame but the contact angle of clamping inlet to seatpost. (=clamping device forces the seatpost to rotate). If thats the case, modifying the clamping device would also solve the problem.
For the time being, i will continue with my fix since it simply worked.
The dust cap covers the shims perfectly, - they are invisible now and the saddle is perfectly aligned when clamped with 5-6Nm.
kind regards