Considering buying a 350D 3.5 rod bender?

[ou2mame]

I have owned an 85 190D, and currently have an 87 300D... I've seen several 350D's going pretty cheap... These cars have changed hands too many times, service history is lost.. is there any way to tell if an engine was rebuilt by MB? Do they put any tags on it? Even if you know where the car was maintained, the dealers won't give you any history due to privacy.