You guys are seriously obsessed as fuck, TheMagicStar included. Why would you care who sang or not... Listen to the music. The 80's were like that, all bands did stuff like this, or most of them anyways. If you want to analyze choruses and find out who is singing what, then you really have a problem.

Dieter or studio 33 have no obligation to provide any "musician" from YouTube, their secrets. These are confidential trade secrets. Not even SIB, not even any other individual that took part in Modern Talking/Blue System can post such info because of the NDA signed with the label.