Just a FYI, the detailing shop up front uses a heavy citrus cleaner, white scotchbrite, and lacquer thinner on heavy spots. You have never seen cleaner leather when done correctly. (Most the heavy cleaning is done with a completly DEAD (read well used) scotchbrite and the cleaner. Lacquer is only for the worst spotting/gunks.
I use lacquer thinner all the time. It removes scuff from other cars, spots in carpet, cleans nearly anything. Key is the application and trained use.
It is then either re-dyed or sealed.