Stereo input signal appears on left channel only

[splatrick]

I have a problem with my input. Some days ago (I think that) it was working properly, other days, after I (re)plugged everything the same way, the right channel of the input seems to be dead. The display mixer then also shows moving bars on the left channel only, while nothing happens at the right. I checked with different cables and also different audio sources. There is no crackling noise, nothing that indicates a mechanical problem. Also the short buzz noise at plugging and deplugging appears at the left channel only. I even tried contact spray without results.
I also did a factory reset, that did not solve the problem.
If I switch to mono, then the left signal is copied to the right correct.
Any Ideas?
Thanks.