Mike, the offset on the 400E 15x6.5" wheels is ET 44.

I don't have the offset specs on the 190 offhand so I can't really say for certain whether they are interchangeable with W124 wheels. I'm pretty sure that W202 (C-class) wheels will not work with W124's or vice versa as the offset is visually different. For specific "what fits with what" wheel applications call Tirerack. They should have such a database and be able to tell you anything wheel/tire realated you'd like to know.

Hope this helps...Lee