Courtesy of the August Horch Museum in Zwickau where I was a couple of weeks ago..
The Trabant 601 was in production unchanged from 1964 to 1990 ( a four stroke model was added in 1989) and all efforts by its designers to have something more modern given the go ahead were rejected, because no money and a waiting list of up to 13 or 14 years.
The makers did try though. Here are two of their prototypes. A Wankel engine (L) and a three cylinder diesel (R). No, I didn’t know either.