In 1988, Ben Johnson was stripped of his Gold. His time was 9.79, which would not have been beaten until Bolt in 2008 - 20 years later. Johnson admits to doping, but also is adamant that Carl Lewis was also not racing clean.
'The Dirtiest Race in History' is a very good book about this race written by Richard Moore.
I read this book about a month ago, it's excellent.
What does it conclude about Lewis?
Carl Lewis is open about at least one doping positive, but he claims it had nothing to do with performance enhancement. Almost everyone in that 100m final in Seoul was eventually connected to doping.