Thre's usually some kind of siphon arrangement that draws conditioner and water out of the tray. It just needs disassembling carefully and cleaning.
Its kinda odd that you missed all the mentions to this problem when you tried to help yourself before asking others to do it for you. A simple Google search should have uncovered many including these:
http://www.diynot.com/diy/threads/bosch-classixx-1200-washing-machine-conditioner-problem.176878/
https://www.youtube.com/watch?v=clg7vwEem78
https://uk.answers.yahoo.com/question/index?qid=20110526225040AAa8ZgA
http://fixed4free.com/answers.php?id=126103
XXX, December 2015